OS has only the GGT10 to my knowledge using a G5 glow plug, OS offer a GT15 and GGT15 in the 15cc range.
The GGT10 is easily convertible to a GT10 by adding a EI ignition (1/4"-32 spark plug).
I prefer the simplicity of the Gas Glow G5 plug for small engines but others will have different opinions.
The GGT10 is a well made engine in the tried and tested OS tradition.