I have a few friends with GMS engines and each time they want to stop it, they have to literall throw the towel in. However, the engine seems to be powerful and reliable once it's adjusted correctly.

I have a TS .61 which is crap and a ASP/Magnum .61 fourstroke which has been very nice... I would say that GMS and ASP/Magnum are the only engines you should buy from China.