Mr G.

As you can see there are many opinions about what to use as a secondary method to shut down the engine (and whether even necessary). You can use either a choke servo or an electronic switch of some sort. I personally think an optical switch is not necessary and therefore use a solid state switch. The choke servo has the added advantage of not having to rig up a manual method, especially on the rear carbed DA.

To each his own.

I hope you got the answer you were looking for.