Personally, I never worry about it.

There are many factors that can contribute to flutter, BUT there are MANY more factors that contribute to a control surface NOT fluttering.

The fact that you have a rounded edge CAN contribute to flutter, but it can also be a factor in preventing a surface from fluttering under different circumstances.

Build your plane however you want.

Fly it.

IF you are one of the rare people who experiences flutter, THEN it's time to make a few changes

(Yes, I know, flutter has happened to a lot of people, but there are many, MANY more people that it HASN'T happened to)