Are gears really useful on an electric bike?

Most Krys bikes have smart motors and controllers that sense how much power is needed for a given speed.  The faster and harder you pedal, the more power is put in by the motor, up to its maximum speed.

Often this power is not governed by which gear the bike rider is using.  On most bikes there is also a throttle which allows the rider to govern how much power is provided.

Where gears come in handy is on very steep hills when the rider might need to assist the motor more than usual to maintain a reasonable speed.  If the battery is run low and the BMS shuts off the battery to protect it from over-discharging then you will also find gears useful.  In the latter case, the gears help out the rider just as with any other geared bike.

Most Krys bikes use Shimano hub gears.  These gears are excellent, requiring little to no maintenance in their long lifetime and are virtually indestructable due to them not being exposed to external damage such as the older style deraileur gears are.  Also, the chain never falls off the hub gears as it can do with derailleur gears.  If you have ever tried to adjust a derailleur gear set, you know how tricky it can be - the hub gears do not need these types of adjustments for the chain moving - hub gears are much easier to maintain and much smoother to use.  You can also change gears while sat at the traffic lights - something derailleur gears don't let you do without lifting the bike or moving forwards.