I've never used snow foam at all, i gind the jet was does a decent job of getting most of the surface crap off, plus sometimes my car gets washed in direct sunlight so i think i'd be a bit worried about the foam drying out before i can rinse it off. 
You are missing out on fun Jimble irrespective of whether it works, it's a very manly thing covering your car with foam on a Sunday morning. It sort of tells the neighbours you are better in the trouser department

Seriously, I use it, but find that if you have driven through wet conditions between washes then you will always have to 'wash' as well. Better waxed the car, the better the results, etc.
I use the AB yellow magifoam just for fun too. I need to get out more.