I use a Weber Summit Gold D. I know its not the same as what you're asking about, but they are fundamentally the same grill, mines just bigger. I'm happy with the smoker box. Now I know this grill is not a smoker, its a grill. So before the purists jump all over me I'll admit that they're right. If you want true smoke you need an offset horizontal, or even a bullet. BUT I'm very pleased with the way Weber designed this. The box is a decent size, I use chunks (chips burn too fast and can fall through the holes) and it holds a fair ammount. I've had no problems getting low. I use just the smoke burner and can keep it under 250 consistent. I haven't tried smoked cheese low yet but think that as long as theres snow around it shouldn't be a problem. The only problems I've had was in cold weather at low flame I wasn't getting hot enough, so I used another burner at low to boost the temp. I try to avoid using the smoker burner at high as it uses up my wood chunks too fast. Overall it is a very well thought out system. One other problem is that the electric ignitor system sometimes gets onery but if you keep it clean it works fairly well. But in my experience this goes for all electric ignitors.
As a grill as a whole, I've had the opportunity to cook an a very expensive big Viking grill and I'd put my Weber Summit Gold D up against it any day.
I couldn't be happier.
If you have any more specific questions I'll do my best to answer them.