Despite seeming scary after reading this FAQ, lipo batteries are far safer than you think. They tend to give you a lot of warning before anything bad happens.
Also, they DO NOT explode. They just don't. They can smoke and vent, but you have to be TRYING to get it to burst into flames.
And keep in mind the advantage of lipo is in it's amperage. You'll be able to actually use the torque of a motor. Otherwise, with a mini Nimh, you'll have to pay attention to what gear ratio you're using.