So they have attracted US clients when they shouldn't have, how does that affect how good a broker they are to use?
Simple. A company that violates the law on purpose or by accident is either a fraud or unprofessional. In both instances I would not trust them. A broker is more than a whimsy frontend with nicely colored buttons that say "buy" and "sell"
I take all your points on board of course, but I have been using them for over a year with no problems and shall continue to do so.