SoundGuyAndy

Whoever gave you that explanation has no idea what they're talking about, or how electronics work. It's because differing pin layouts mean that the Canon flash or cable is shorting the pin that supplies power to the little flash that comes with the camera to another pin. The short circuit caused heat and likely damage to at least the camera, and maybe the flash.

I briefly tried the Meike, but in addition to the aforementioned swivel limitations, it was very flaky in terms of having to be exactly lined up with the contacts juuuuust right. It also didn't like being used on a cable at all. Cheap flashes = pretty loose tolerances. I've currently got a Metz 44 AF-2, mostly because I needed a TTL flash for a job before the m400 was shipping, otherwise the extra bit of money buys a nicer interface, slightly more flexibility in functions, a full 180 degrees in both directions (the 44 is only 120 to the right), and even smaller size. My m400 will be here Monday, and then I'll decide if I keep the 44 as a backup/second, or sell it, since I'm missing the return window by a couple weeks (sad trombone). While they do require an update for HSS, which Metz promises basically ASAP, the update can be done by you, with a USB cable, and that's worth a lot to me over the Nissin. The i60 was compelling as a more powerful, wireless option for not a whole lot more, but considering that I'd have to send it in for an update when HSS gets added to it soon, and if any new issues arise, well, Metz is getting my cash for now. Given the transient state of flash on Fuji right now, I really can't overstate the value off that USB port.

Don't use glue. Use two part epoxy, and be sure to roughen the surfaces of the caps with coarse sandpaper first, and then thoroughly clean them before using the epoxy. Properly mixed and cured epoxy is stronger than the plastic. I've got a pile of these in my camera bag. That said. OP/TECH finally had their version out for XF mounts, with an added O-ring seal on each side. B&H has them in stock. $16 ea, so about double the price of two third-party caps, if you don't value the o-ring and not accounting for a few dollars for a big syringe of epoxy, your time, and the smell of fresh epoxy. The math of how much that's all worth to you I'll leave as an exercise for the reader.