A Rx LiPo Cutoff is a great way to send a car tearing off into the woods. At that point you're reliant merely on the throttle return spring, which is supposed to be a worst-case-scenario option, not something to rely upon. Never mind brakes.

If you're worried about over-draining your LiPo, you're not charging it enough, or running some puny undersized capacity LiPo. It's just that simple. Charge it more. Or if you want to physically run the battery to its limit, that's just dangerous and reckless.

I'll gladly take accidentally over-draining a $20 LiPo over destroying a $400 engine and potentially hurting someone.