If belts are coming off your car you aint putting it together right to start with
As for diffs blowing up. I have seen diffs coming out of the NTC3 here that were totally disintegrated. The more power you strap in the worse the damage on the diff becomes.
Only company I seen turn to shaft drive are Kyosho. Belts are still the only way to go in Nitro Racing and always will be.