The only problem I have had with the system at LHR is when the light operator assumes we are taxiing faster than we actually are (doesn't happen often, when it does it is usually when we start moving after stopping, single engine taxiing means we don't accelerate very fast) and the stop bar comes on before we (quite) cross it. Even with this, it is still better than any other airport I have ever been to.
Keep it.
If they get as far as running a trial without it, I can imagine the delays caused when every aircraft stops at every intersection and asks for directions. And as for the RT congestion caused by everyone asking for progressive taxi instructions...