There have been quite a few studies on the effect of rounded, tapered and squared trailing edges surfaces. Some I've seen were quite well done in a scientific manner (wish I had kept the source) which, to me at least, pretty well proved that squared edges were best, sharply tapered next best and rounded the worst in so far as contributing to flutter onset. More important points than trailing edge shapes though are surface stiffness and making sure there is no slop or play in the servo to surface connections. Every surface will flutter under the right stimulus if it has any mass at all and gets the stimulus to start the flutter.).