After fooling around 0.21 a bit I find the change of the SAS behavior doesn't cause any problems for me on the rocket part, the SAS work as intented, spaceplane is a bit different, stock spaceplane works fairly well, but I do get a bit of pitching motion when thrusting forward, all in all I find the new SAS much more "gentle" then the old one, and I am happy with it. TBH you have to be very careful that your craft don't spin too much that it max out your control vector because the new SAS will always fail at this rate, then again, if you managed to built yourself a rocket that you need to max out your control to keep it stable, you better off just learn how to put a rocket together from the start.