I want to use this to record horse riding videos of myself.  Would the P2 work for this?  If so, how far away will it track?

Check out videos on YouTube - you won't see anyone on a horse unless I've missed something, but it will give you some idea of what is possible.  Currently opinion among users is that the tracking on the Pocket 1 is actually better, but I'm sure an imminent firmware update will bring changes.  One limitation would be that to start the camera recording you would need to be within range of the phone you are controlling it with, unless you have someone assisting you - in which case the assistant could do the shot manually anyway.

Hi, Equest. The maximum distance of the head and shoulder track is 5 meters (within 3 m when tracking for the first time). The size of different objects is uncertain, making it hard to estimate exact distances. The initialization box is required to be no less than 1/10 of the screen size.