I have had an HW100 for 5 years now. When I got used, I sent it right out to Alan Zasadny for tuning and a moderator. He also fitted a Styer barrel he had laying around to it, custom machining it to fit the HW100. The gun is very,very accurate and fast. My experience hasn't been without issues. I have had to have the regulator resealed and the breech plate O ring is a bear to keep sealed, I go through one of those every time I remove the barrel for cleaning (yearly strip down and clean) but it isn't that big a deal to change, since the gun is a modular design. My only gripe besides the breech seal is that my thumb hole stock isn't adjustable. An easy fix perhaps this winter as a project. I have shot a friend's BSA R10 and found it "gritty" in function but highly accurate. Either gun, you really can't go wrong.
Jamie