I just finished converting a Spot Ajax with the Bafang 750watt BB motor and a 48v 11ah battery.
it came out fantastic. Lots of power.
the Bottom Bracket drive is superior to every hub motor out there, because it allows you to run all that power thru whatever gear set you want on the rear.
the Spot comes with an 8 speed Alfine hub... Which is okay, as long as you don't input torque lower than 2.1:1... And as long as you back off power when shifting... But I will be swapping out the Alfine for the more robust Rohloff, or a NuVinci.
even as is, tho, this motor powers up a 28% grade under throttle alone, no problem.
the Bafang is also amazingly quiet. Thus far, very impressed with its performance.