There are also all kinds of issues with systems like these. Inference is the biggest one, which causes the light not to move/follow the person/s. Then there are issues like the light following the wrong person, not quite on the person all the way depending on angle, hitting tilt/pan limits and leaving the person in the dark, and the list goes on.
I remember seeing it once on a show and the ME and board op cursed the system because of the issues involved. Board op was constantly have to control the fixtures manually on the fly. The ME had to try and get the system working each and everyday.
Long story short, not really worth it. Get a follow spot, they really have no limits covering a whole room, position limiting, and will always be spot on if you have good people running them. Pardon the pun
.