Re using the AMNPS with charcoal, I have been experimenting with using it and the 6" tube smoker on the wood pan in my Camp Chef LP smoker. This because I have had problems keeping loose pellets and wood chips smoking when I have the box temp set in the 225deg range and it is shirtsleeve temperatures outside. The burner flame is just too low to keep things going.
Thinking inadequate oxygen might be an issue, I did an experiment where I brought a piece of 1/2" black pipe from a hole in the back wall of the cabinet to the center of the wood tray to give added oxygen. The pattern of burning pellets told me that oxygen was adequate; the ones right near the fresh air source didn't burn any differently than the ones well away from it. I also tried a 3' extension on the smoke stack to increase draft but no joy there either.
The AMNPS works well, but basically all the pellets burn at the same time. I don't remember the burn time but it was maybe 3 hours. Definitely much, much shorter and much more smoke than what I get when I cold smoke with it.
With the 6" tube smoker, I get about 2 hours of reliable smoke, so that's what I'll probably start using.