Their high end servos are good. dont buy the cheap ones. I talked to a full ride trinity guy that said if I knew which company they came from I wouldnt hesitate. I used them before in a MT nitro 8thscale and was an awesome servo for like $50, tons of torque and good speed. They have heatsink servos now to that look decent, but they aint cheap.
TT MT4G3 all tricked
TTST4G3 MT4ed out
I use a bluebird servo in my RC8e and just bought 2 more for a new SC8e and 1 as a backup. I haven't had any problems and they are fast and strong. I broke a horn on a bad landing and no problems with the servo. So they are reliable also. Go for it!
last year i bought a bundle of 5 new 631mg servos.
One was faulty from the beginning and i got a refund.
I broke the "ears" of one of the remaining servos in a silly accident: i flew off the track with my touring car and landed on the grass.
The other three are performing like a charm.
If i have to find a negative point about the 631mg servos, it will be for the plastic they use for the servo case: it is too brittle.
Some of them don't come with enough grease on the gears so if you get one with a clear case look to see if the gears are lubed enough. If not open the case and put more grease in. Also some of them need lots power from the Rx to operate properly without stuttering so you may need to run a power capacitor on the Rx.