+1 to Izzy's comment about getting one with a cable.

I have an old "Portawattz" 300 that I may have bought at Costco many years ago, and it has a 3 foot cable. This has proved itself very valuable and useful. My Forester has 3 12 volt outlets: dash, in the panel between the seats (hidden inside the compartment, but with a cable run) and in the back. The all in one would only fit in my outlet all the way in the rear. I have used my inverter in all 3 because the cable fits anywhere.

Since it has lasted about 10 years, I guess you could say I'm happy with it. It stays in the car at all times.