The idea behind a Throttle returns spring is the return the throttle to neutral in the event that the receiver / servos loose battery power. The TRS does you absolutely no good in the event of out of range or the tranmitter dies. This is because the servos still have the power to overcome the spring. This is where the failsafe works.
I learned this the hardway about 15 years ago when I was racing 1/8 Gradn prix. I hit a cement wall at around 100 mph not much was left of my car.

Anyway if anyone want to look at a TRS setup on the RC10GT, there is one in my Gallery.