Gotta agree with NWH mate, you seem to be yet another cobble-together-and-sell-it-to-window-cleaners-cos-they-dont-know-any-better merchant.
What you have there is a tank, a merlin unit, a DI vessel, pump and battery and some hose (and that all-important dab of glue thats holding the tank in).
That aint a system, its a DIY job. If you'd done it for yourself for your own window cleaning (I think you are Booysen Pro Cleaning in Catterham? Googled your phone number), that would be fine. But now your trying to sell your DIY job as a system for an over-the-top price.
Also, it don't look safe at all
Why do window cleaners continually think they'll make a fast buck by selling diy job "systems". We're all smarter these days, I dont think you can get away with it now.