Their geofencing API seems to advertise tracking users. It seems to provide some kind of metadata storage alongside a geofencing API. My guess is that some websites are tracking their users though this API.

I haven't dug into it much further, but if their API is used for tracking, it should stay on the list.

Edit: looks like they provide a dashboard to follow the location history of any user using their API. Yeah, no, I'm adding this to my personal blacklist just in case.