Thinking about it the ankle is a pretty clever Place. My wrists are very often in different orientations to my body, but my ankles are more or less always in line with the way I'm facing.
Downside of a belt is that you have a much longer way around your body, which means longer wires, and perhaps an easier chance of breaking something. A belt also implies pants that can accept a belt, which probably wouldn't work for a lot of people, at least not every day with every type/style/color of clothing.
The anklet is reasonably unobtrusive, and unless you are wearing form-fitting pants, you can keep it under your pants leg to keep it out of sight. Even if you're wearing tighter pants, shorts, or a skirt, and you don't mind the under-house-arrest tracker vibe, it's still wearable, and might make for a fun conversation topic.
Agreed that the belt is better from the standpoint of what the device is for, but I think the anklet is a bit more practical. I know I would definitely wear it more often (more or less all the time), but I could not say the same about a belt.
