I am not so keen on having a button which could trash the engine if pressed in flight. Say you are trying to reach something on the back seat and kick it with your knee… it is in the right place for that.
It needs a guard e.g.
I think I agree with Peter on this subject, a switch guard is required.
However I see little need for this bit of kit unless you fit the whole electronair ignition system.
could trash the engine
Too lazy to check what engine your TB has, but methinks that “only” the starter and flywheel would be in danger. And yes, my ship sports a starter button with side guards 
IO540-C4D5D.
I did a google on Apollo Lunar Module engine start switch, and got some ideas on how to make it hard to press it by accident, and also how to label it 
The engine won’t be startable unless you have main power on, but the only interlock (to prevent starter activation when airborne) I can think of would be bus voltage under 26V (main alternator voltage regulator is set for 28.0V and the backup one is set fo 26.5V) but you can’t do that without “electronics” even though it would be only a few components.
I would definitely replace your keyswitch…
The timing to turn the key ccw on short final to shut down the engine and lower the gear looks tricky to me;)
Bolkow Junior has mags key but not start. A separate guarded push-button operates the starter.
At first I often nearly broke the key twisting it trying to activate the starter.
Can you not buy an aircraft mags and starter switch? They’re available.
It’s been pointed out that this dual-switch thing makes it difficult to check that the ignition is dead. Fuellers and hangar crew like to see a key removed. And I agree.
Peter wrote:
It’s been pointed out that this dual-switch thing makes it difficult to check that the ignition is dead. Fuellers and hangar crew like to see a key removed. And I agree.
Have a set of gym keys on a linyard for that purpose? :)
Peter wrote:
Fuellers and hangar crew like to see a key removed.
Whether the key is in or removed doesn’t prove or change anything. I would also trust two separate mag toggle switches like the example below more than the innards of the rotary switch.
Peter wrote:
It’s been pointed out that this dual-switch thing makes it difficult to check that the ignition is dead. Fuellers and hangar crew like to see a key removed. And I agree.
I can see the reasoning, but our aeroplane has switches for mags and a push button starter (unguarded, albeit not in a position likely to be pushed inadvertently) and I have never ever had an issue with anyone on the ground feeling uncomfortable by the lack of a physical key.
