Despite some excited reviews on this product and its peers, I felt that it would be unlikely to clean effectively the acres of decking that I am saddled with. A friend however was singing its praises and said "try before you buy", so I did. He loaned me his and I was instantly converted. I cleaned our paving slabs outside the front door (approx. 6 sq m), the same type of slabs in our courtyard (approx. 20 sq m) and untreated wooden decking (approx. 60 sq m) in less than a day. They hadn't been cleaned for 2 years, because (through bitter experience of working with the normal power washer lance) I had been dreading the job, yet instead of the two and a half days that I had previously taken I had it all done in less than a day. It's a miracle! I placed my order with Amazon the very same day - especially since their price seemed to be half of that in the high street outlets!
You do need to keep it moving, because if you leave it in one spot it cleans almost too effectively (in a very characteristic pattern) so keep it in motion but, boy, what a great job it does!
I had also been confused over the differences between the models - Karcher don't make this very obvious. The T200 has the black plastic composite handle tubing, whereas the T300 uses what appears to be some sort of alloy (metal anyway). In view of the level of use for it, that I envisaged, I plumped for the cheaper plastic version. The difference in performance, of course, is nil, and I actually look forward to cleaning the aforesaid paving and decking on a more regular basis - a little and often, as they say - because the job is so quick and easy now instead of inching along with the 5cm wide power washer lance, being very careful not to miss bits. There are other more expensive models, I believe, but quite frankly, at this price, and with this performance, why would you pay more?