I look back over 40 years of flying, thousands of flights and about a hundred airframes, all of equipment failures i have had. And a lot of this flying was done on am transmitters with converted/homebuilt gas motors and non-resistor spark plugs.. The first ten years was done on a homebuilt blue max kit radio, next 20 on various futaba am and fm transmitters, then to 2.4 jr about 10 years ago.

A couple of batteries fail open circuit- total loss of planes
a switch fail inflight after hundreds of flights- total loss of plane
A nearly new jr hd switch fail on the ground- whew..
a new receiver with a defective solder joint, glitched like heck inflight no loss thankfully.
An ignition fail and ruin a receiver by the spark jumping across to the radio switch. 1 inch of separation between the switches. Happened on the ground for the final straw but the motor started running erratically a few flights before it went pop. High voltage can do a lot of weird things..
An intermittent open circuit in a battery that i caught while recharging- one battery took zero and the other took several hundred mah..

With this in mind i try to use two batteries, two switches, and i don't mix/ get anything control wise near the ignition system..