Synpower, like every Valvoline PCMO, uses an entirely different add pack as compared to M1 or any SOPUS oil.
UOAs show good results with this oil and oil life for the API SN formulation appears to be the equal of any other OTS syn.
I've used it in the past and will likely buy it again, although as with any other oil I currently buy, it would have to be FAR.
I have around five quarts of Synpower left.
Maybe I'll dump it in the Focus and run it until the end of November, at which time the car will get some FAR Ultra 5W-20 for the coming winter.