We have a CTD570-2. This was bought as a solution to our contract cleaning requirements before we got more seriously involved in Carpet Cleaning.
It is OK for spotting and occasionally cleaning smaller areas. It does leave carpets rather wetter than is ideal, regardless of the amount of dry passes.
We do still use this on some of our non-CC contract work where the customer just wants a quick once over and as long as quick drying isn't required then it is fine for that.
Plus points: small, convenient, easy to transport / handle / use, adequate on small jobs, fine as a spotter.
Negative: small (thus low capacity of both solution and waste), relies on heat from water supply, messy / unhygienic to empty waste, low PSI on solution, leaves carpets a bit too wet, not a serious machine for a professional CC.