I have 3 trx4's and had a trx6 for a few years and have yet to break anything other than wearing out a factory brushed motor.
I did have one front drive shaft fall apart due to a loose screw that I'm pretty sure the 12yr old Korean that assembled it forgot to tighten. They seem to be pretty...
I have the axe system in a trx4 and love it. Excellent performance. I also run a puller pro in my vanquish vs4 10 paired with a mamba x and love that too. I think the puller pro is marginally better, mainly with low speed control, but unless your a 'technical' kind of crawler guy, I'd go...