As I posted on the F90 forum, the mass balanced F90 has flown successfully without flutter. Unfortuneatly the fix included upgraded HD control horns so the experiment doesnt really prove that the balancers are the solution, maybe part of it at best. No signe of any strange quirks as a result of the balancers design, which was questioned by at least one person who thought they would induce turbulence. So far so good...