I noticed this on ebay and was very tempted until I have just read Darrens comments on here.
We have two Ionics systems, a Pro6 650ltr Thermopure and a Pro5 650ltr cold system, both bought second hand with vans.
The only problems I have ever had with them is one of the level sensors went off, £22 to replace and a pump had to be replaced on the cold system (£100 ish).
The Ionics DI cannisters last us around 6 months at a water reading of 280ppm in our area.
The Thermopure is a tremendous system and I would buy another without blinking if the price was right and it was all in good condition and working order.
Guess I may give this one a miss! Cheers for your honest comments Darren, did you con him out of £3100 or not, probably not as it's a good set up and the Pro7 filter should be able to be bypassed to turn it into a standard Pro5 Thermopure