I bought one of these on the recommendation of Philip Reeve (on his blog). I already have a couple of other old Pentax lenses that work extremely well.
Apart from being an exceptionally good cheap lens (it works very well indeed on the A7rii), it works better in infrared than any other lens I have; a lot of lenses develop hot-spots at smaller apertures, but this one is free of hot-spots at any aperture. Taken on an IR converted Sony Nex 5N (665nm) at f8. It's had a touch of Topaz Glow in PP.
Angel by Jon, on Flickr