Does anyone know of a good comparison between the various fitness-tracker device companies that notes what their API policies and own-your-data stances are?

I don't turn up much. A few complaints about FitBit from 2013; not a lot that's current. I'd like to think that the contemporary competitors in this space have more to offer than pure, grinning-evil vendor lock-in, but so far I don't see a lot of evidence to support that.

And no, I don't have any desire to cobble together a halfway-functioning Borg addon made from Arduinos, 20-gauge wire, and exposed AA battery holders. I mean real products.