out of interest, how are you planning on using the ultra pure ro ?
is it so you can fill really quick at home with no static tank and minimal space needed, or are you planning on transporting it with you for bigger jobs and topping up your 400 ltr tank during the day ?
£5000 seems alot but you'd have a top system and super efficient from the sound of things, and people have spent the same sort of money in the past for ionics systems.
I must admit if I had the income to justify it and was needing a new system from scratch I'd be tempted given my living situation (1st floor flat, no garden, no garage/driveway or even dedicated parking space or outside tap)