My experience with SMM 10 is pretty positive. Today I turned it on on my way to work. It was 1 hour of driving. My device is not overclocked, running PR 1.2 firmware and default SMM settings. The device is not overheating (in fact it was not even warm), the application runs smoothly and did not crash on me one time. Phone was connected to the bluetooth car kit, I had an incoming call while the navigation was on, everything worked fine. I also made it to reroute a couple of times as I took the other way that it was instructing me - it was fast and reliable.
So I'm glad I made the update to SMM 10 after all