An in-tank heater is pretty much a basic standard in the UK. Maybe the US has lower amperage ratings or some other regs that prevents its use on domestic circuits so it can't be used?
The switch panel on the side of that machine is different from the UK spec.
I'd email the supplier and ask them if they would supply a dual 3-stage vac WITH heater to a UK customer. In-line heaters must be great for high heat needs on bigger jobs but dragging one around and setting it up on every job? Must be a right pain, I'd soon get fed up of it!
Those pump pressure ratings don't match the ratings of the Shurflo pumps that Ashbys supply to the UK market. Not sure if they'd be the same quality or not but it's a proper pain changing the pump, mostly due to getting the hoses on and off the spigots.
Would be an idea to ask them what make the pump is.
A 500psi pump might have a lot higher flow rate than the vacuum performance can deal with. Finding out the flow rate as well as the pressure would be handy. I think the 135psi UK-spec ninja flows at 1.4L/min but someone pls correct me if i've got that wrong.
The tanks aren't huge, you'll be forever refilling and emptying with the pressure/flow cranked up and also risking overwetting. I find the 135psi machine is very well balanced with the flow/recovery, simply upping the volume of rinse isn't necessarily going to be "better", quite the opposite probably. On some jobs though I reckon it could handle a bit more pressure/flow so the 150psi might be a good option
The water lift is great, brilliant for a portable machine. But airflow is just as important and is a bit pants on this type of machine, around 100cfm I'd guess. Obviously that's no different from any other m/c with twin vacs in series. I wouldn't recommend going over 50ft of hose, only in dire emergency and very slow dry passes with the wand. I keep mine at 25 as much as I practically can, you can tell the difference even between 25 and 50. The reason for that is because you're relying on the lift rather than the airflow to extract with, every extra foot of hose you add on increases the size of the space in which the motors are creating a vacuum, thus impeding efficiency.
To be honest if you're happy to spend 1500 bucks on a machine, you can pick up a perfectly serviceable one over here second hand. They do come up fairly frequently, I picked up a Ninja a few months ago with twin 3-stage vacs, 135psi and a heater run off a separate cable (so it can still run when the motors are running) and paid 700 quid for it.
Any portable will do, ignore the name on the outside, it's the spec of the vac motors and the pump that determine how good it is, everything else is gravy.