So only 250W, but if I'm correct isn't the Bafang a crank drive system? I've only had experience of hub motors so I'm not familiar with the power delivery characteristics of a crack drive but Watt for Watt will a motor delivering its power via the transmission path pull better than a direct drive?
It'll give you much better torque at the wheel than a gearless hub motor (I assume the double freewheel transmission helps avoid wheel-spin), as well as the off-power efficiency of a freewheel. There's generally a weight saving, too, but that's not really important here.
From experience of hauling ~60kg of trailer with a 37kg trike (plus about 80kg of me) with a 250W motor, I reckon it'll make the acceleration tolerable. Hill climbing will be underwhelming with a full load, but they're using them in flat places anyway.
