I've had four electric bikes but all lead-acid so no chance of disguising them. Although one had its batteries incorporated into a topbox on the back, the large hub housing the motor was the giveaway. Lithium Ion is a game-changer in this respect along with more compact motors, allowing designs...
And how many of those actually have pedals capable of propelling the machine? No pedals = no bicycle. Similarly, power output has to be restricted to 250 Watts whilst powered speed limiter needs to be set to 15.5 mph max.
They are not illegal if they have passed similar construction standards to petrol motor scooters. I presume your's hasn't, and if you are using it on a public road then you are driving without insurance. If you don't have a motorcycle licence, then you risk losing your car licence which you...