If you just want something to wash your car, then pretty much anything will do the job. The bottom end Karcher K2's used to use plastic components rather than metal which made them failure prone, but i'm not sure if that's still the case.
If you want to clean your patio/drive/decking etc, the the Home Karcher versions are decent enough. I've got the K4 Home Premium version:
https://www.johnlewis.com/karcher-k4...g&gclsrc=aw.ds
Done the trick so far, vario lance to adjust the pressure, dirt blaster lance and the whirly thing for the patio.
Then just add these:
http://www.ebay.co.uk/itm/Karcher-K-...EAAOSwyvBV9soG
http://www.ebay.co.uk/itm/Valetpro-D...wAAOSwBnVW9Atf
