greygore
That being said, it's fast by the standards of treadmill desk usage (judging by what I've read and a coworker that bought her own treadmill). I can't speak authoritatively but the impression I get is that most people walk around 1.0 mph which is maddeningly slow for getting around, but appropriate for mindlessly pacing while typing or talking on the phone.
It works particularly well for me, but your mileage may vary (literally). I tend to walk fast (2.0 mph) which means I need light clothing and a fan blowing on me. That seems to be faster than most people who walk (and beyond the speed you should start at). I'm also able to walk longer than a lot of people do (I've walked a marathon distance several times during 24 hour hackathons). Contrast this with my partner who found it almost impossible to work while walking.
I tend to pace when I think, something about walking helps me think; my treadmill allows me to stay at my computer where I can still write code or make notes, versus getting up from my desk and wandering away. This really helps me switch rapidly between deep thinking and focused working.
Two things I highly recommend if you want to take the plunge: make sure you position your keyboard and monitor(s) carefully as it makes a huge comfort difference, and use a trackpad over a mouse. I've used my Magic Trackpad and had no problems controlling my cursor, but the few times I tried to use a mouse I found it very jumpy (especially at my faster pace).
If you're unsure I recommend looking for a used TR800, take a lot of breaks, and start slow. And a quiet fan can help keep you cool.
Additionally I tend to pace when I think and this means I can stay at my desk while puzzling something out. The fact that I can burn a thousand calories on an extended day of focus is just icing on the cake.
I see my treadmill desk as something that helps me work, not a substitute for the gym. Maybe dial back the judgement and "harsh wording" in the future, or at least talk to people before developing and/or sharing such a strong negative opinion.