All I can say is, the GRP got so much attention due to a lot of US drivers using them. At our local track, the OS is the choice to use. Very few use the GRP and even at that, I have seen some have issues with it and it hasn't had any performance to write home about

If I wanted an italian mill, Novarossi would have been my choice. GRP & Axe Rossi are family member spinoffs, but they have some engine goods traits in their engine building IMO. GRP just got on to a bigger distrubutor than Axe Rossi did. But at least Axe Rossi brought a EUROs title to their brand name.