Mervyn

Judging by the wear on the lens my 23f1.4 is definitely my most used one. :-)

Optical and mechanical quality of the 90mm are near-perfect. And the 90 has a certain magical quality about it that's very addictive and hard to define. The 90 is optimal for headshots and outdoor portraits. But it's less flexible and is less practical to use; you'll need to adapt to it. Indoors you may bump into walls and outdoors you'll need to walk a lot more whilst composing the shot compared to shorter focal lengths. For indoor and low-light use the 56 is better and for flexibility the 50-140 zoom would be the better choice. However, the 90 is easier to focus with then the 56. And compared to the zoom it's rendering is better suited for portraiture; I find the zoom a bit bland compared to the 90. Also the 90 is much smaller, lighter and cheaper then the zoom.
 
For low light use the 56 is king. And the zoom has such incredible OIS that it easily beats the 90. For the 90 I usually use 1/250th or faster. With the zoom I can go as low as 1/15th, or with subject movement about 1/80th.
 
One other reason that people trade in their 90mm besides practicality and flexibility could be the rattling sound that it makes while it's off camera, or while the camera is switched off. This is by design and not a defect. It has to do with the autofocus motor which uses magnets. The magnets are not activated when they have no power, thus the rattling sound of the lens interior. Just don't worry about it, it will be fine. No, really! :-)
 
Personally I've sold my 56 and kept the 90. The 90 better complements my other two lenses (16-55 and 23f1.4).
 
One last word of advice: The 90 definitely is not a telephoto for photographing birds or other small animals. For that I find that even the 100-400 with the 1.4 teleconverter can occasionally be a bit short.

Check out the reviews of the Mitakon 35 f0.95 on the BHPhoto product page:
https://www.bhphotovideo.com/c/product/1226781-REG/mitakon_zhongyi_mtk35m95m2fx_speedmaster_35mm_f_0_95_mark.html
 
Especially read 'Not really f/0.95' and then 'I stand corrected'.
 

I'm a happy prime user, but you're right that a zoom can be very convenient. I enjoyed photographing with a zoom during our summer holiday and it's great that it covers everything from wide to normal to a little bit tele all in one lens. And not having to switch lenses on a stormy beach with lots of sand blowing around is an added bonus.
 
However, I think you should give your primes a chance. Just pop on a 23 or 35 (my favorite is the 23) and leave all your other gear at home. I find it fun and quite liberating. Also I tend to get more creative because I need to move around more to get the shot when I only have one focal length.
 
The only times when I really feel I'd need a zoom is when it's crowded with a lot of people and I'm unable to move around freely to compose the shot. Or when I'm inside and I can't go wider because I'd be bumping into a wall when I'd step back.
 
For everything else the 23 is great. It's also cool for very dynamic portraits with a much more 3d perspective as opposed to say the 56 or 90 f.o.v. which normally make things more flat. The 23 f.o.v. is more energetic whilst the 56 or 90 usually are more flattering and more still. Things I'd most likely never have discovered if I'd only have been using a zoom.

Optical and mechanical quality of the 90mm are near-perfect. And the 90 has a certain magical quality about it that's very addictive and hard to define. The 90 is optimal for headshots and outdoor portraits. But it's less flexible and is less practical to use; you'll need to adapt to it. Indoors you may bump into walls and outdoors you'll need to walk a lot more whilst composing the shot compared to shorter focal lengths. For indoor and low-light use the 56 is better and for flexibility the 50-140 zoom would be the better choice. However, the 90 is easier to focus with then the 56. And compared to the zoom it's rendering is better suited for portraiture; I find the zoom a bit bland compared to the 90. Also the 90 is much smaller, lighter and cheaper then the zoom.
 
For low light use the 56 is king. And the zoom has such incredible OIS that it easily beats the 90. For the 90 I usually use 1/250th or faster. With the zoom I can go as low as 1/15th, or with subject movement about 1/80th.
 
One other reason that people trade in their 90mm besides practicality and flexibility could be the rattling sound that it makes while it's off camera, or while the camera is switched off. This is by design and not a defect. It has to do with the autofocus motor which uses magnets. The magnets are not activated when they have no power, thus the rattling sound of the lens interior. Just don't worry about it, it will be fine. No, really! :-)
 
Personally I've sold my 56 and kept the 90. The 90 better complements my other two lenses (16-55 and 23f1.4).
 
One last word of advice: The 90 definitely is not a telephoto for photographing birds or other small animals. For that I find that even the 100-400 with the 1.4 teleconverter can occasionally be a bit short.

Optical and mechanical quality of the 90mm are near-perfect. And the 90 has a certain magical quality about it that's very addictive and hard to define. The 90 is optimal for headshots and outdoor portraits. But it's less flexible and is less practical to use; you'll need to adapt to it. Indoors you may bump into walls and outdoors you'll need to walk a lot more whilst composing the shot compared to shorter focal lengths. For indoor and low-light use the 56 is better and for flexibility the 50-140 zoom would be the better choice. However, the 90 is easier to focus with then the 56. And compared to the zoom it's rendering is better suited for portraiture; I find the zoom a bit bland compared to the 90. Also the 90 is much smaller, lighter and cheaper then the zoom.
 
For low light use the 56 is king. And the zoom has such incredible OIS that it easily beats the 90. For the 90 I usually use 1/250th or faster. With the zoom I can go as low as 1/15th, or with subject movement about 1/80th.
 
One other reason that people trade in their 90mm besides practicality and flexibility could be the rattling sound that it makes while it's off camera, or while the camera is switched off. This is by design and not a defect. It has to do with the autofocus motor which uses magnets. The magnets are not activated when they have no power, thus the rattling sound of the lens interior. Just don't worry about it, it will be fine. No, really! :-)
 
Personally I've sold my 56 and kept the 90. The 90 better complements my other two lenses (16-55 and 23f1.4).
 
One last word of advice: The 90 definitely is not a telephoto for photographing birds or other small animals. For that I find that even the 100-400 with the 1.4 teleconverter can occasionally be a bit short.

I agree, hands down. As perfectly wrote by Mervyn, it's called "consumerism". I'd call it anyone "ability to resist".

This is my set-up, I love these primes, previously owned and sold these before buying them again.

I had the 35 f1.4 at some point. Though the image quality was great, I couldn't quite get used to the noisy auto-focus motor.
 
When I heard there was a f2 version I did some bokeh tests to see what the difference in wide-open depth of field was. Just a simple test, nothing solid or scientific. Under the circumstances i didn't actually see very much difference between f1.4 and f2. I also tried f2.8 and that was a difference; i liked f2 better.
 
Also I find the 35 f2 actually has a very pleasant kind of bokeh. It's very smooth. And it's fast and silent with WR as a bonus. The faster AF speed is very helpful for photographing small children. My daughter has a tendency to run up straight to the camera so it won't focus because the distance is too small.
 
The X-T2 supposedly has better low light performance. So for photographing kids, personally I'd pick the f2 over the f1.4.
 
For the 23mm I love the f1.4 version. I haven't tried the f2 version, because I don't feel the need for it. The 23 f1.4 performs fantastic on the X-T2! It's a lot more responsive then it was on the X-T1 and somehow it seems to focus with much more precision as well. The noise of the 23 doesn't nearly bother me as much as the noise of the 35 f1.4 did.

I had the 35 f1.4 at some point. Though the image quality was great, I couldn't quite get used to the noisy auto-focus motor.
 
When I heard there was a f2 version I did some bokeh tests to see what the difference in wide-open depth of field was. Just a simple test, nothing solid or scientific. Under the circumstances i didn't actually see very much difference between f1.4 and f2. I also tried f2.8 and that was a difference; i liked f2 better.
 
Also I find the 35 f2 actually has a very pleasant kind of bokeh. It's very smooth. And it's fast and silent with WR as a bonus. The faster AF speed is very helpful for photographing small children. My daughter has a tendency to run up straight to the camera so it won't focus because the distance is too small.
 
The X-T2 supposedly has better low light performance. So for photographing kids, personally I'd pick the f2 over the f1.4.
 
For the 23mm I love the f1.4 version. I haven't tried the f2 version, because I don't feel the need for it. The 23 f1.4 performs fantastic on the X-T2! It's a lot more responsive then it was on the X-T1 and somehow it seems to focus with much more precision as well. The noise of the 23 doesn't nearly bother me as much as the noise of the 35 f1.4 did.

Apparently there is a firmware update, but you'll need to send the flash in to the distributor for the update.
 
https://www.dpreview.com/forums/post/58344264