The adaptor itself seems to work fine. I've used it with lenses like the Helios 44M 58mm and Helios 28mm wide-angle with much success. However after shooting with it for several days, I've noticed maybe a dozen fine metal particles covering my A7ii's sensor. I can't be certain whether the particles came from a lens or the adaptor itself, but it might be a good idea to leave one of these adaptors on each M42 lens you have, or purchase a more expensive one that won't wear.
03/05/2018
Excellent adapter, does exactly as it should. I can now use my selection of M42 lenses on the Sony A7ii the way they should be used.
11/02/2018
04/12/2017
Good machining shame wasn't the one I needed a lot of forums misleading about the adapter I needed but will use soon when have the right lenses
03/12/2017
I waned this to test my old glass on a Sony FS5 camera and it worked perfectly.
16/11/2017