RE: Hirtenberger .61 with a sliding piston carburetor
You should not use an idle bar glow plug in a schnuerle ported engine, well only as a last ditch effort. Glow plug recommendations are a lot like carb setting. There is no one glow plug/setting that works for all. You need to set the engine up and test with a tach. But as a general rule if you are going to use low nitro fuel start with a hot glow plug.
I know just about nothing of the OS brand of glow plug. I had a full set of Rossi glow plugs that I used to set up my engines. Once I found the one that ran best I then looked for a cheeper version in an other brand.