Some of the mech mods like the SMPL ones do not even have a Delrin ring in the top. So if you have no atty on and hit the fire button or the atty unscrews and you hit the firing button... Direct short...
the other thing is that with a slightly protruding center pin on the atty 510 the top of the battery may get dented in a bit from overtightening or dropping the mod or the 510 pin gets pushed up in the atty just a bit and then you have the top contacting the 510 threads... Another direct short.
Again I do not think these types of mods should be sold.