I have a chemical guys Foam Cannon (Cannon for PW, Gun for Hose as Brandon pointed out). Differences between brands is dependant really on who makes it. You want one that has a solid tank not thin and flimsy and fittings of brass/steel not plastic.
It's a great tool to have to prevent swirling or marring the paint when washing. It does not eliminate the need to hand wash a daily driver in my findings (people think you can foam on, spray off and vehicle is clean). It keeps more soap on the vehicle meaning less chance of dragging something on paint and causing those paint issues.
My method for my fleet of black vehicles is power wash the dirt and debris off, foam the entire vehicle down, hand wash with three bucket method (one soap water, one clean rince, one just for wheel soap and wheel tools), power washer off, dry with leaf blower and drying MF towel.