Yes, do it!! They work awesome. I have a MTM foam cannon. Not only does it work great it's fun to watch the neighbors look at me weird while washing the cars.
I haven't used one, but I've heard a lot about them. I've heard that they add intense foam to the car during every wash. I've once seen my friend washing his car with a foam gun. The foam gun mixes the soap, water, and air to create a thick wash foam. It was just amazing and I'll soon purchase one.