Hi,
We've recently bought one from price cleaning supplies. Has nearly paid for itself already. We needed LOTS of purified water for a some hospital courtyards where obviously we couldn't have trailing hoses through the corridors and trolleys etc would have meant filling up every ten minutes, luckily each courtyard had an outside tap.
It also means for large commercial jobs you can leave two guys on site without a van and they can work all day.
It is a bit of hassle needing a power point but they are fantastic machines which will produce purified water quicker than you can use it!
Cheers,
Huw