Our BBJ has the HGS model 4000 by Rockwell Collins as well. Alteon (Boeing) told us at training that it was allowing some operators to takeoff at a lower RVR.
It definitely does help during a low vis takeoff, especially when you lose an engine just after rotation. The autopilot does just fine for landing though, except for the lack of a rudder axis which the HUD also gives you (via your feet). I'm still not sold on it though. Maybe if it were on both sides?