I've got an electric mountain bike which has a claimed range of 20
miles (my commute is 10 each way so I can't verify this yet as I charge
the bike again at work before the return journey).

I can comfortably cruise at 20-25 mph on mine without breaking a sweat
- which is the reason I purchased it as we do not have showers at work.
It appears I can travel an extra approx 5-10mph faster than other
riders I come across on my commute who are riding hybrids for the same
effort.

My bike is more geared towards pedal assist rather than twist and go
and it is for this reason why it more resembles a normal bike in looks
and weight. If the motor is switched off I can still ride it normally
which I suspect maybe difficult on some of the more heavier and
powerful models.