The weight of the engine's weight is placed low and centralized in the frame (instead of a heavy hub in the front or rear wheel). This gives a better balance and a better balanced feel.
Probably fewer broken spokes from hitting hard surfaces, potholes, etc. than with a heavy hub motor in the wheel.
Often a bit lighter than equally match hubengines. Depending on construction that is.
The engine can use the bicycle gears. That means that it is possible to keep the electric motor at a speed which better utilizes the battery, meaning more effectively. In other words: That can provide longer range if used properly.
By using different gears provides a wider range of performance from a smaller and lighter engine.
A lot easier to change a flat tire with a non-electric hub motor. The wheel is easier to carry, etc., everything becomes easier, no electric cable to mind, etc.
Climbing steep hills better than a hub motor.
Wheels without hub motor rolls normally better downhill. It feels more like a bicycle. And we like that, don’t we?
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Cons of a mid-drive:
Often harder to get to fit the frame. It might not fit your regular bike frame etc. More complicated. Bosch system even need a special frame.
Often more expensive than a simple hub-motor.
Can be noisier than a hub, a direct drive with a good control system is quiet. More parts, gearwheel and such that makes more noise than a totally brushless engine with no gear.
Mid-units have more moving parts and therefore tend to be less reliable than most hub motor kit.
Might hit something hard with the engine below the frame. Hub engines seams more protected somehow. Or?
