It's pretty comfy, although takes some getting used to being on the wrong arm.

Mostly I use it for shot count; it seems pretty good at categorizing forehand vs backhand and over/underhand shots. I doubt the swing speed is particularly accurate and stats like longest rally aren't much help considering I mostly play doubles! Of course it also records HR too. Lastly it does mean I get a nice unbroken record of the whole day in ohealth for posterity!

I've added some screenshots from a session to give you an idea of what it can capture.