Richard, were you using hot water with those machines?
I would be afraid of using hot water with those as they are plastic but I don't know if they are the kind of plastic that can handle the hot water.
I saw those videos on youtube and it looks like it left the areas a little wet, not totally dry or mostly like vacuum surface cleaners but it looked like there would not be any puddles left behind. How dry/wet was the area when you were done?
It looks like interesting technology, and I am guessing that with your 4gpm machines, there was no problem pushing the water through 50' of the 1 1/4" hose?
I also wonder how far it will push the water?
I have a sludge pump using basically the same technology but instead of the jet being horizontal spraying out the back of the surface cleaner, the sludge pump has a jet spraying vertically causing suction but using all the flow of the pressure washer to do so. After about 1' high more or less then the hose starts to lay over and lay on the ground. I have 100' or 120' of the pool hose (not sure if it is 1 1/4" or 1 1/2" hose) but it will suck the puddles down to about 1/4" or 1/8" quickly and push it out the hose no problem, even on a slight grade up hill.
I think if you had a separate pressure washer hose for that nozzle that shoots out the back of the surface cleaner (need to modify that surface cleaner plumbing if possible) and keep all your flow for the cleaning, you could probably run longer hose for discharge.
Or
Run a larger pressure washer or just "T" the 2 machines together and put a larger nozzle in the outlet port to flow more water and put nozzles slightly larger into the cleaning nozzle fittings so you can clean a little bit faster.
I would like to see a video of this surface cleaner cleaning larger areas like outside parking lot, sidewalks or other areas to see how wet the area is as it is cleaning.