I have experimented with the showerhead foamers. I like them for triple foam applications. I tried them for presoak and lubricant
soap as well.
They save some chemical because you don't have the full tube of foam draining between cars but I don't know how significant that is. They typically use more holes but smaller holes than the tubes making it easier to apply foam that rinses easily.
Probably the biggest downside is that they don't cover the lower rocker panels well and if customers are watching from outside the car they may not like that. They are also expensive to retrofit. I got around the cost factor by buying just the showerhead part from Vaughn Industries. It was much cheaper than Sonny's and I used the foam generator and mounting brackets I already had.
David