I have (had) both.. Fiido M21 not badged the same brand, but Engwe is the same.
Fiido M21 clone has slightly larger frame, so the minimum seat height is higher. Single pivot rear suspension is simpler & more durable.
I sold the Fiido M21 clone because it has spoked wheels, with the 750w peak power output I think if you use that often the spokes will get stressed.
Engwe has cast wheels, may be heavier, but more durable in the long run for the power output.
Performance wise they are both very similar. Hydraulic brakes are nice, but a bit overkill for me (170 lb. rider).
Engwe has regen mode, it doesn't generate much, but still extends 2-3 mile of range to limp you home or to an outlet.
I personally have no need for torque sensor power output, I know not to mash the pedals or use the throttle when I'm shifting to avoid damage to drivetrain. Both ebikes come with throttle, so torque sensor seems unnecessary to me.
Fat tires will kick up lots of water when ridden in rain, even with the fenders that come with these ebikes, I would invest if extensions to the OEM fenders.
They are both heavy, may be challenging to lift & fit into car for transport, even when folded.