If you are registered, you get access to the members only section, can participate in the buy & sell second hand forum and last but not least you can reserve your preferred username before someone else takes it.
I have one which I use primarily for astrophotography.
With regards to ergonomics, this lens belongs on a tripod, preferably with a soft weight like a bean bag on it to d&en vibrations. If possible, it is preferable to prefire the mirror to reduce vibrations from mirror slap. It is not impossible to handhold, but I would guess it would take much practice to be able to get usable results doing so. At 500 mm focal length any movement is exaggerated.
What are your requirements vis-a-vis optical quality? The MTF diagrams are available on the Hasselblad web site, if you are interested. If one takes care in their shooting, this lens is very good, but few have the patience to shoot at this focal length.