I see no mention of the fact that lots of people who swore by treadmill desks also started swearing at them after about 6-9 months.

The problem is that your head is supposed to move when you are walking. When you are working at a computer, your head has a fixed point that you are trying to make stable. This is simply untenable posture and causes all manner of problems.

I wonder if that kind of problem holds for just standing, though.