Hi Vic,
In my career as 'battery abuser' running my speed boats in competition, I must say that Lipo's are much user friendly than NiMH, which are really high maintenance and have a much shorter lifespan than my current lipo's.
It goes without saying that you'll have to treat the batteries right, something that applies to any type of battery chemistry.
Over the years I've switched all my models from NiMH to Lipo's without a hitch.
The trick is to use suitable chargers, an ESC suitable for lipo's (with a lipo cut-off to protect the battery from over discharging) and common sense running the model.
If you have seen the video of my MAS, the boat can run at this speed for close to an hour, due to the large capacity I installed.
In fact, I'm 'recycling' Lipo's in my scale models that I've ran in my competition boats for one season, after which the capacity tends to drop off and these lipo's are no longer fit enough to give me sufficient runtime for seven minutes full throttle.
In my scale applications these 'second hand' lipo's don't even get handwarm, even at full throttle, as the ampdraw is substantially lower.
When I reduce the amount of full speed running, the runtime of the MAS is over three hours, I don't last that long...
For a smaller MTB, brushless motors are ideal, either inrunner or outrunner, the latter having my preference due to the better low end response compared to inrunners.
Regards, Jan.