In theory, blutooth has a range of about 10 meters.
In practice, if the controller is inside a metal box (the van) and there are other obstacles in the way etc, I think you'd be lucky to get 5 meters.
I know this becasue if I leave my phone in the van, and just use the bluetooth headset (and believe me I've tried nearly every one going from £10 to £200) you get 5-6 meters away and it cuts out. Vans are just signal killers for this sort of thing.
Still I'd be interested to see how this thing performs, its a good idea. However, even assuming it works further than that, the question I have is:
would I start fiddling with my phone to control flow etc? Honestly, no I wouldn't.
But that's just me, others might find it convenient.