I hired on from local co op, wasnt that cheap once you brought the shampoo etc. but well worth it. Did a lovely job on carpets and rugs came up lovely and newlooking but think it may depend on the rug material. Didnt do the stairs or use the attachements tho sorry
Some professional carpet cleaners poo-poo them because they want you to think that you need to pay them a lot of money.
But, I know a pro who uses the commercial version (identical, only slightly larger tank and a different colour) and says they are very good. They have a way of agitating the carpet in an up-down motion that is nearly unique. Used properly (google this before using to make sure you're going the correct speed) they are very good.
Professionals with truck-mounted machines can extract more powerfully, leaving carpets much dryer, and they know which chemicals to use on stains or fouled areas, but I think a Rug Doctor can be quite good.
I rented one and was happy with the results. Months later, went to get it again and it wasn't available (rural Highland community = not a lot of options.) I ended up renting a Karcher that did a fine job of extracting, but without the agitation of the Rug Doctor, it was noticeably less effective.