I'm happy with everything I've gotten from Autogeek, including my foam cannon. You just order whatever fitting you need for your pressure washer with the foam cannon (might have to take a look at the wand on your washer). Basically it'll just replace the metal tube that goes into the wand.
The advantage to a foam cannon is that you let the foam start to lift and lubricate grime. Then you wipe it down with a wash mitt and avoid scratches and swirl marks. A good wash mitt, in a bucket with a grit guard, is a must have.
I rinse with the pressure washer, then foam cannon, wash with mitt and shampoo, rinse with pressure washer again, dry with air dryer and drying towels & detail spray/wax as you dry. Takes me 45 minutes (but the Opticoat makes the process easier and faster).