It looks like this wheel is using a standard quick release. If that's the case it would be fairly easy to take out. Couple of options though:

- When locking the bike, run the lock through the wheel. Yes, someone could still cut the spokes and steal the main hub, but this is going to take q fair amount of effort.

- Have a bolt on version, lots of older bikes, or bikes which use a horizontal dropout design already have this. Typically they use 15mm wrenches, but there are some alternative sizes (some even use hex keys).

Looks like a pretty cool concept. I personally would prefer a model which only gained energy from the rider when coasting down hills or braking, then could release the energy at the riders discretion. Plugging a bike into an external power source isn't something that interests me.