I've bought this lens with Nikon mount. It took some time to adapt it to M42. Last weekend I took it with me and tested in the field.
Overal about mechanics: very long, but not so heavy (about 2kg). Trigger focus is easier than standard on lens ring. I tried it only with bean bag.
Overall about optics: sharper than K 500/4.5, much less CA. In most cases I don't see any CA. Very natural colours. Not so nice bokeh. K500 has much better bokeh.
Pentax K20D ,Leitz 560mm f/6.8 Telyt-R
1/320s f/8.0 at 560.0mm iso200
Pentax K20D ,Leitz 560mm f/6.8 Telyt-R
1/800s f/8.0 at 560.0mm iso200
Pentax K20D ,Leitz 560mm f/6.8 Telyt-R
1/500s f/8.0 at 560.0mm iso200
Pentax K20D ,Leitz 560mm f/6.8 Telyt-R
1/1000s f/8.0 at 560.0mm iso400
more shots are
Leitz 560mm f/6.8 Telyt-R Photo Gallery by Piotr Sobolewski at pbase.com