My wife is giving serious consideration to getting a treadmill desk, as a way of getting exercise while she’s stuck working on her computer. Does anyone have any first-hand experience with one of these?
ETA: I’ll settle for second-hand experience. 
My brother (prez at his company, BTW) has one and from what I hear, he uses it all the time - even on conference calls. He loves it.
I have no idea what model he has or anything else - most definitely second-had experience.
I have one. I used it when I was working from home through chemo. It’s the WorkFit, available on Amazon.
Overall, I liked it. You have to manually adjust the tension but I didn’t find that to be problematic. It’s very quiet so no impediment to making conference calls, etc. Biggest downside is that the mouse doesn’t work well because the desk is angled and gravity moves the mouse for you, so you have to use the laptop’s finger mouse, which is a tad tricky when you’re moving your legs.
I personally thought that the cushion in front was too wide; I would have preferred something thinner so that the keyboard was closer to my body.
And I’m not sure how I would have felt using this in an office because it was pretty narrow so getting in and out of it was not the most graceful thing I’ve ever done.
Anyway, the WorkFit was priced right at Amazon and did the trick. Note that I never worked so hard that I was actually sweating; I was just using it to get my heart rate up a bit.
FYI, I paid $75 for the Amazon folks to put it together.
I’ve used one a few times; while good in concept, I hated it.
I’m usually a faster walker. To walk anywhere close to a normal cadence, I’d get warm in the office. Therefore, the only way I could use it was to move at such a slow cadence that it was unnatural. Many people can comfortably walk 3 mph / 20 mins a mile; that’s slow for me. However, over 1 or 1½ mph I found my body heating up. I found it more effort to go that slow because your either taking baby steps or pausing between each step.
I’m a ditz. I thought the OPR wanted to know about fit desks. I see now that she wanted to talk about treadmill desks. I’ve actually had experience with those too. At my old job, they had two nice ones. When they worked anyway. The feature that raised the desk up and down based on the height of the user kept breaking down. I can’t imagine how frustrating it would be to have to call in a service guy every time your personal tread desk broke down! Of course, if it was your own you wouldn’t have to keep raising it up and down.
I found that they were really good if you were trying to read or listen to something such as a conference call, however if you needed to type, forget about it. It’s just not natural to walk or run and type.
Of course, that was one of my biggest criticisms with the tread desk because it stopped you at 3.0 or “safety reasons.“ I found that to be too slow. You could go faster if you bypassed the safety feature, but management really frowned on that.
So, to summarize, it’s OK if you’re needing to read emails or read reports. Not so good if you’re wanting to do things that require extensive keyboarding. However, I did find that working for a half an hour or hour on the treadmill put me in a much better mood than just sitting at a desk all day.
I second all this - I use a treadmill desk daily, and absolutely love it. It’s far better than being stuck sitting or even standing all day.
I too have found that it’s good for conference calls or email or deck reading, but not if you’re going to be doing a lot of typing or high-concentration work.
There’s a lot of evidence that sitting for 5-8 hours a day is bad for our health on a number of metrics, and I always feel better going back to the treadmill desk after the occasional “ass-buster” all-day meeting where I have to spend all day sitting down.
I made mine myself, affixing a bookshelf board to the flat arms of my treadmill plus the central strut between the grips with string. I wrapped the arms in foam and tied it into place so the “desk” shelf isn’t jolted. It works fine–I’ve used it for years.
You’ll want a treadmill that is well-rated as a walking (not, or not just, running) because she’ll use it at low speed when working.
ETA: 2.5 is my non-sweaty walking speed on account of my short stature. I can send email at 2.0 and compose text easily at 1.8.
At least one study has shown that kids going 1 mph at school had higher energy at the end of the day and lost 8# average compared to desk-using classmates at, I think, 6 months.