I have had the chance to shoot a couple of examples since starting this thread, and have to say I am impressed with the feel and accuracy of these guns. Despite the weight (or because of it?) they feel very stable and easy to shoot. The accuracy is very good and the impression I got was that the wind didn't have as big an effect at 55 yds as my S400 or EV2 (this is only an impression, would need to shoot one for a couple of months to really tell).
I am suprised that there are virtually none being used in FT this winter (in MFTA I haven't seen one!) though the HFT league has a few mostly in the hands of youngsters. I think with so few people competing (where have all those sold gone?) it will be a while before we have a definite answer as to how good the AR20 really is.
EV2 mk2 with 2009 big Nikko
HW97K with 6-24 Nikko Nighteater