I've installed several multi-product foam gun systems. The latest job features PS, Tire, and Bug/MagChloride cleaner.
Each product line is plumbed to a manifold directly above the bays...along with an air line. Product changeover time is negligible because the liquid lines are always full.
For cold climates, I add an "anti-freeze" line to the the manifolds...and the trough is insulated and heated.
The systems work great. Owners report significant increases in usage and positive comments from their customers.
A big advantage of these systems is the elimination of all those high pressure check valves in the plumbing trough!