Yes,Ive got an ignition key switch situated between the controller connector and the controller. It saved the controller once.A while back I was connecting the batteries to the controller when BANG!!! Somehow the controller connector shorted out,the darned thing was burnt black and the actual metal parts of both the connectors were sorta melted out of shape.The 25 amp fuse had blown as well. Thank goodness for the keyed switch...I've replaced the connectors on both sides and all's been fine since.If it wouldn't have been for the keyed switch I'd have been shopping for a new controller.
My controller is completely enclosed in the metal battery box and I haven't experienced any failure due to heat.Summer's finally arrived and the temps where I am are getting past 30 degrees celcius,the controller gets fairly warm but not so warm that you can't keep your fingers on it.But your setup may work differently,mines a brushed motor.
Definately get a keyed switch,could be a controller saver.Oh yea no spark when connecting the batteries either,an added bonus!
Eric