I have a Vax cafrpet washer - not the most up to date model, I purchased it about four years ago.#
It works carpet. I have never managed to get the gadget to do stairs to work, - gave up - had cream carpets on my stairs in the house and before I moved out I had a professional carpet cleaning carpet.
When I moved into my flat there was a old, expensive carpet throughout. Not to myj taste but wanted to keep it for a yjear whilst I decided what I wanted. Problem ws teh Living room area had sort of black grease type marks on it quite prominently. Spent the first few weeks cleaning those with th vax machine, and much to my surprise, they all came out eventually.
As the only carpet I now have is one in my main bedroom.,do not have much use for this now. However, my daughter used it on the absolutely disgusting carpet that was appeared beneath all the rubbish in the bedroom, when one of her teenagers moved out. Again, did take three or four applications, but came up okayj at the end of it.
I would say they do the trick, and once purchased are therefore quite cheap to operate, not as wonderful as they show on the demonstrations, but perfectly good.