I have the Max Power engine in both 10th and 8th scale, the 21 size Max Power (Novamax), I can probably say it is one of the best engine out there at least the one I have! hehe
now just to give you some comparison, the Novamax powerband is different from RB, JP. Kind of in between the both. RB C5 Rody or Collari more like a On/Off switch, in sane bottomend, and as for the JP R1 Kangaroo it has insane top end, it just rev like there is no tomorrow but sort of lack of bottom end punch and that can be solved by lower gearing, later clutch engagement or even smaller size tires.
But overall, the Novamax is an excellent engine for all around, and honestly if I come across another Max, I would get it again in a heart beat!