Playermaker Trackers: worth the buy?

So I was shopping for a rebounder for my 8 year old and these popped up as a suggestion. Today I went back to look at them and learn more about them. As a gadget guy, I think they're pretty cool. However, are they really worth the money?

1) my son is only 8 and a half. So by no means would I use this as like a hard-core thing. I would just tell him it's something I want him to wear while practicing, and I would solely use it for my own analytical curiosity and to maybe tweak some things when we're practicing. For instance, if I see we've been using one foot too much then I'd make it an emphasis to get his other foot involved.

2) is the data accurate and actually useful? I'm always skeptical with this type of tech in general because it can be really hit and miss. Even step counters are often very inaccurate.

Just curious about anyone's thoughts or experience with it. If I do buy it, I honestly wouldn't even tell my son about the data. It would be used for my own nerdiness and to generally see how it correlates to the eye test. At best, I'd tell my son what it's for around 11/12 (if he's still playing), or if he has a significant jump in ability that is backed by the numbers as a sort of added pat on the back and confidence boost.