Am not sure but I believe its compatible with most DSLR 

I use one on a Pentax 24-70mm filter size 82mm. Just make sure you buy the right size for your lens. I have the nd1000, and I am very happy with result. They also sell adaptor step down for your other lens. 

Yes. I have the same lens and adaptor on my Sony a7ll and it works beautifully. The m42 is also known as the 'universal' mount as other 3rd party camera and lenses also used it. I own 6 other K&F e-mount adaptors to different lens makers (ltm, MD, CF/CD, Nikon) and they all are well built with a nice snug fit. Highly recommended. 

I actually have not received this adapter yet. It's shipping from China. Don't think that was disclosed in the ad. However, I do not believe this is for the Pentax Q body rather for digital and film cameras that take the Pentax K mount in its many variations. So I'm expecting to be able to mount my Leica M mount lenses on my digital and film Pentax K mount cameras, no autofocus or relay of exposure information, only to be used with manual focus and exposure. 

1. Canon DSLR mount(Canon DSLRs, e.g. Rebel Series, 700D 650D 600D 550D 7D 60D 7D etc) is called EF, usually expressed by EOS, and Canon mirrorless camera(Canon EOS-M mirrorless cameras like M1 M2 M3) was usually expressed by EOS M
2. Nikon DSLR mount(Nikon DSLRs, e.g. D40 D70 D3100 D3200 D3300 D5100 D5200 D5100 D7100 etc) is called AI or F, usually expressed by Nikon/AI, and Nikon mirrorless camera(Nikon 1 series mirrorless cameras like N1 1 V1 V2 V3 S1 S2 J1 J2 J3 J4 AW1 ect) was usually expressed by Nikon1