GMS has been around for well over 15 years that I am aware of. They originally just rebadged ASPs but then Jim Goad (Indy RC) got together with a couple others over there and designed the next generation. Those were really good engined at the time but never really sold well. Kinda like early Magnums.
The newest of the GMS line are VERY good engines and well worth the money. People who bought the Raptor found out just how good they could be. Unfortunately, Tower made it part of their contract with GMS to not sell that engine to anyone. At least, this is what I was told when I attempted to import lots of them.
Although I am no longer selling engines, I still have several GMS sizes on my shelf waiting for suitable airframes.