Spring return bolt systems generally have a very high initial bolt speed. At the time the bolt starts moving and picks up the ball to push it into the barrel they can be very, er, destructive, shall we say.
With the Etha we implemented a 2-stage bolt acceleration profile so that initial bolt force is considerably reduced as well as adding the solt tip to the bolt.
The people who can give you the best feeback/input about this would be the guys who have been using them with tourney grade paint. If you look in THIS
thread there are some reviews from players that have shot all kinds of brittle paint through their Ethas.