Yes you can turn it down on the transmitter, very handy for younger kids when they're just learning to drive. It's not the same for all RC's though. Some cheapies won't have that function, but then they're unlikely to be very fast models any way.
The XLF I would also not recommend. My friend has one & he broke it within the first 15 minutes. He fixed it up, brought it out again a week later and then it broke again, in a different way, in the first 10 minutes. Baring in mind that these were only pretty minor crashes it was really quite disappointing for my friend, who is also fairly new to the hobby. Now I know everybody's experience will differ, but because of what i've seen I would just stay clear of them. They aren't much cheaper than the Quantum any way, which quality wise is leaps & bounds above.