I ordered my Samyang 12 mm f 2 last week and I'm waiting for it any day now.
When I shot 35 mm I used to have, and have a lot of fun with, a Nikkor 20 mm, so when I decided to buy a new lens for my X-E2, I actually looked at the 8 mm fisheye as well, but my decision toward the 12 mm f 2 was almost immediate: as far as I'm concerned, more versatility, more ease of use for an amateur photographer as I am, in the end, more fun...
I'll let you know my impressions on the field after it arrives and I start using it!
Ciaooo,
R