Mine's a Mavic Pro, it doesn't follow a sensor on you, it uses optical recognition on you and follows you, but it's admittedly very limited, tops out around 40MPH, can sometimes lose you, etc...
I.E. Good for parking lots or even maybe around a track or something, but not for use on the highway or anything...
More on it was back in this thread (As well as some tracking videos)
http://www.valkyrieforum.com/bbs/index.php/topic,94138.0.html