DD motors are of course less energy efficient at low speed compared to geared hub motors.Does that experience include CST/BPM and clones?
We've already established the G310 is not up to the job and it's looking like the CST clone is the best option for what he needs. A 1000W DD is just going to be illegal (unless he gets it thru an SVA, has MOT/insurance/licence and wears motorbike helmet), inefficient and he'll probably have to swap out battery packs every 10 to 20 miles.
motor wear is also subject to riders weight, style etc. The figure I gave is an average. I usually replace the whole clutch and nylon gears, so the fault could be either clutch or nylon cogs.
Most of the clutch / nylon gears I replaced are BPM motors.
They are supplied mainly to heavy riders and high milers like deliveroos. This said, my most successful deliveroos bike is the Rio FB with 3" wide tyres, Bafang G06 motor.
I have not replaced a single clutch unit on it yet.
The G06 is also available in kit. The Rio FB is not in production at the moment.