I just received my Pentax K-mount adapter for the Sony E mount. Seems to be well made, but lenses fit extremely tightly on it. You get what you pay for, I suppose - $7.
I also bought a new spanner wrench with tips for $20. Both from the same Chinese merchant.
I'm going to try it tomorrow with some Pentax K lenses: 1.4 50mm, 2.8 28mm, 40mm pancake. I think that I might do a 50mm lens comparison test (a la Brian Sweeney), but I'll need to get some more lens-mount adapters to really do it right: Olympus OM, Minolta MC/MD, Kyocera/Yashica Contax, Leica M, Zeiss Ikon Contax RF/Kiev, Nikon F, Canon FD.
I wouldn't mind trying the Alpa Macro-Switar - the only lens that I have ever call "exceptional." I was thinking of the Contarex, but at a certain point, a Planar is a Planar is a Planar.
That could be fun.