It's not entirely plug and go. It connects to the factory-standard plug's wiring. Instructions call for you to REMOVE THE TANK to run the acc. plug wires up to the front. I'm not sure that is really necessary, but the bigger issue is that with the BMW kit you are still tied to the 5-amp limitation of the factory plug circuit.
What I did was get
this kit from Powerlet Products. I connected direct to the battery, removed (easy) the aluminum side cover of the tank, and ran the wires up under it's lip, between the aluminum and plastic tank.
Then I put the plug on the left side of the beak:

This plug gives me 15 amps, more than enough to power my Gerbings stuff, GPS, etc. Also, the plug is always hot. Some guys install a relay into the other plug's line, so the acc. plug is off when the ignition is off.
I actually have a BMW accessory plug kit that I haven't installed yet. My idea is to try pushing a fish wire under the tank, and just pull the connector wires through, then tie-wrap it in place up as far under as I can reach.