I've run the Powermaster for a bit over a year now & like it.
Have v good batts, 1-0 cables, & the engine's 19:1 - really spins my 6.5 over. Did all these things plus manual glow extension to help the lower comp start reliably in the winter, and it the plan worked.
Started it once @ -8 F, w/o engine heater just to see if I could depend on that if necessary. Otherwise it'll usually get plugged in when it's that cold for less wear-n-tear.