My K&F Concept MD to NEX lens mount adapter has already broken after three days of use. Lenses attached to it no longer lock into place. The bayonet mount still keeps lenses on but after focusing or changing apertures, I have to make sure to tighten them back on now. It still works but broken in three days? A bit disappointed to say the least. It's too big a hassle to send it back; I'll use it until it fails altogether then get another. A million years ago (well, more like 35 or 40), I had a cheap 2X teleconverter wear out in the same way, but that was after several years of use. Other than that, it still works like a charm, and would be a 5 star item were it not for my example's fragility This setup won't threaten fully automatic digital photography, but being able to take digital photos with my 40 or 50 year old Rokkors is just too cool an opportunity to pass up.
Update 5Feb2021: Now the bayonet mount flange to the camera for this thing is loose and has rendered it useless. Hassle or not, back it goes to Amazon. Probably will be considering another maker. Shame. It looked great on my camera, but less than a week of use has completely worn it out.