I have a lower model MyTee from Clean Freak, and after a couple years, I'm still very happy with it. I bought it primarily for cleaning carpet puke spots from our previous and current rescue dogs. But I also use it for car carpet detailing as needed.
I didn't get heated water, and honestly I don't regret that. But I don't use the extractor in a typical way. Here's my style for both house carpets and cars. Keep in mind that I am not a professional and thus, I don't need to work in the most efficient way possible (time is not money for me when carpet spotting).
I've seen over the many years in dealing with carpet, that residue is the real issue. So my technique is designed to minimize residue.
I always put just plain hot water in the liquid tank, and I have a couple spray and squeeze bottles of various shampoos and detergents.
I start by vacuuming the carpet to get loose stuff up (unless it's fresh barf). Then with the spotter I spray some hot water to wet down the area. If it's lightly soiled, I pull that water up with the extractor. I then spray shampoo or detergent as needed. I work that in with my fingers or a soft brush. I then extract that. I then lay down more water and extract. I inspect and repeat the shampoo if needed (typically not). At the end I then repeat the water treatment at least one more time. I always finish with one or two rounds of hot water and extract to make sure the carpets are clean.
Having just water in the extractor spray container has always worked well for me. I haven't noticed a big difference between hot and room temp water, but I rarely fight really dirty carpets.
Lastly, I have to say that the MyTee that I own (a low model), is built really well and has held up well for the last couple years, but I don't use it all the time.
Sheldon