Thanks Mondie, I think answered above but yes, it's supposed to loosen the dirt so more comes off with the jet wash.
I have a Nilfisk jet washer and the attachment was less than £20 off Amazon, plus about £16 for the foam, which will do many washes as you dilute it down.
It needs to 'dwell' for up to 10 minutes and don't let it dry on the car.
Worth a try I reckon.