I am using 3 of the HS-635HBs on the tail feathers of my 33% Bücker Jungmeister and really like them. The centering is excellent and they are very fast. I'm using HS-645s on the ailerons, 1 per side, 2 ailerons per servo. These are very good servos. I use Hitec servos on all 3 of my Warbirds and have never had a problem with them. I haven't seen the need to go to digital servos.

Ken