It's the little cart with the 3x 20" RO's on it, 500l per hour £3850 yes?
Maybe it would be useful on a really big Commercial job with difficult access for the van, totally useless on Domestic. What you want is one of their RO Van mounted systems. If your round is mainly Domestic, with a little bit of commercial, I would say get the 500l system. And even then, I wouldn't buy it from them but from Purefreedom or similar.
If you have an estate now, sell it and buy a van, that is in my opinion the only way to do wfp window cleaning properly.
And yes they do say a van system can't come close, but they would wouldn't they, at £3850 a unit. You need to hook it up to a water and power source, while with a van you just park next to the building and start working. Even if it would be a static unit, a 4040 RO to a 1000l IBC in your garage would be miles better.