I initially had problems with the gears stripping on the handheld unit. I used it vary carefully at all times. Looking back though, I did have a problem with the button sticking which did not help matters when it was flooding - but I was quick to remove the unit when this occured. I have since removed part of the bezel from around the button and have received a new set of free gears from HPI.
I was using my Makita in the meantime which worked fine - use low torque settings if you do this. Recently, I started using the rotostart again with no problems - maybe it was just a fluke - donno.
Overall, I don't think the quality Rotostart's drill unit is comparable to the quality of the Savage 25. As long as you are careful, you will probably be OK. In other words, you won't get away treating the rotostart like you do the rest of the truck.