[Gordon Steadman]

Probably depends what motors you are using it with and how much time you spend on full throttle. If you go slow, you are using the resistors in the controller to reduce the current to the motor. Rather like an electric fire, putting current through a coil (resistor) makes heat. At full throttle you effectively bypass the resistor.

I use an MRRC 5ohm controller with hot rewinds and have to hope the heat is only 3 to 5 minutes. I've had blisters on my hand before now. I use a thumb controller so the resistor is vertically about 1mm from my palm. At least the DS resister is at the top.

You might consider a transistor controller if the heat bothers you - more money of course!