I have one and I think it is a pretty good piece of kit.
Tests just about everything on my clk including things like window motor current, limit switches, lamps etc - even gives part numbers and software revisions of major modules.
Even gives generic obc engine codes.
One bug I have seen is that when testing some sensors it will give the correct reading and then a few seconds later give the full limit reading -eg temp 10 deg then temp 255 deg - as long as tou know this beforehand it is fine.
One thing to be aware of is that you need to be able to 'read' the figures and know what the correct values should be under normal conditions.