Installing the lock behind the seat tube is pretty fiddly. Doing it with the rear wheel off would make it easy, but getting the rear wheel off and back on is quite the job. Just use the hex key and some patience.

Buy yourself an 18 mm open end wrench too. If you rear flat, you'll need it, and one wasn't provided with the bike when I got mine. The motor wires come out through the axle, so a box wrench won't work and a semi-open flange nut wrench won't work either. (too thick)

I think these still come with Slime in the tires; that's a great touch too, considering what a b1tch it is to fix a flat.