I have used the Thunder Tiger/ Ace S1903 servos. They're very comparable to the other brand name servos. If you can buy them at a better price than Sanwa, Hitec, or Futaba servos, then there is certainly nothing wrong with using them.

It sounds like your HS225MG servos would work fine in a typical .40-size trainer as well, so long as you can make a servo tray to hold them.