Mid drive motors on the bicycles are a very efficient way generate assist, it measures your input at the exact point power is being introduced to the drivetrain and adds to it.
The motors are matched to gears and tuned to operate in a much more efficient manner, electric motors are most efficient while turning higher RPMs so when compared to hub based motors they can achieve higher real output for less watts and power consumption.
measuring the power of a system based solely on watts can be very misleading as the overall efficiently of the system is what happens in real world riding, some manufactures are very deceptive in this regard using numbers that are peak, max or just plain made up rather than safe operating watt ranges that can be maintained for time of the ride.
The motors weight around 8lbs and with the weight low it keeps the bike feeling natural.
The frames have to be made for the motor that is used, you cannot buy or retro fit these systems aftermarket.
They are fine for wet weather use, riding them in the wet will not hurt them they are well sealed, submerging them is not a good idea they are not designed for that.
Both Bosch and Shimano have a 2-year warranty on the motor system.
On mid drive motor systems the rest of the bicycle uses all normal bicycle parts and standard service procedures.
Modifying or tuning the motor or battery system with non-approved parts voids all warranty’s.
When traveling with the Mid Drive systems in wet weather Bosch recommends removing the battery and putting these aftermarket covers on for additional protection , driving through heavy rain at 70 mph with the bike exposed to the elements is a bit like using a pressure washer on it , best to give it a bit of extra protection .