I use the Vax stuff – mine came with 3 litres free which despite the cats' best efforts I've yet to exhaust. I think I bought another couple of litres having neglected to notice the free offer when ordering direct from them. Anyway, you only use a splash in the tank. I am sure you can use any kind of non-foaming detergent, it just squirts it on the carpet and vacuums it up.
It's a bit of minor palaver to set up and clean after use (well, five minutes or so) but not something I'd do at 3am*, I still keep some Doctor Beckman's patent carpet cleaner on hand, and unleash the machine at a more civilised hour.
*mostly my wife and I compete to not hear the cat throwing up and pretend to carry on sleeping. I am better at this. For this sin, she does the nocturnal triage, and I do the proper clean. Cats, as a rule, do not throw up at sensible times.