I just got a foam cannon on Tuesday. I put some Mr.Pink soap in it from Chemical Guys, and blasted away on my Camry. It looked like a foam grenade went off in my driveway.
It had a nice dwell time before it started fizzing off, so I had plenty of time to get my 2 wash buckets ready. I then hit my car with nothing but water to get the foam off, then hand wash. If you've never used a foam cannon in your driveway, be prepared for rubber-neckers driving by....like looking at an accident on their way to work.
My wife liked it enough to say "do mine", and she almost never let's me wash her car.
If you do buy one, get it from amazon. It's cheaper, and its the same one that AG sells, minus the logo on the cheap bottle.
If you have a standard pressure washer quick-connect fitting, your good to go. If you have an electric washer, your gonna have to fine a connector that fits your style/brand of fitting. AG sells them, and they include ine if you order from them.