Power is by no means the weakest engine, even the best 4s engines are very weak in comparison, however they are not high speed/perforated motors like rcinpower wasp majors or toa turbine motors. Efficiency is 8+ minutes with a lightweight 5" build, Fpvcycle sliding with a 20x20 stack is highly recommended, freestyle until you get bored of each pack. Smoothness - You will almost eliminate the need for your gopro Hypersmooth, very smooth motors. Durability - Seems to be pretty good, bent from diving into a steel tower but was able to straighten it out, bearings stayed good enough to keep using it and it didn't fail. Balance. Overall terrible motors, best to keep in stock so I can build more quads with them.