I couldn't find torque information on the TRU page.
$20 seems reasonable for a smart servo but I'm not very impressed with the communication protocol used by this system. If I'm reading the protocol correctly it has a very slow transmission rate. I'm pretty sure you can't take advantage of the Arduino's UART to communicate with the servos. I think you'll end up with each transmission blocking the program.
I think determining if these smart servos are worth the bother and money will depend on the servos' performance. What sort of torque to they produce?