The auger length is a good question. I am guessing it is as long as it is because it’s an obtanium build. Also because he wanted enough height to be able to drop char into a pail. But it’s probably also to provide a seal against having a significant air inlet to the bottom, with enough oxygen the char would burn to the bottom.
The concept looks scalable, I believe it could be made a lot smaller using smaller biomass, straw or wood chips.
If the combustion was enclosed in a refractory lining, the burn would be more complete. A chimney would create quite a lot of draw / draft, allowing the burner to be throttled over a range with a damper.
Forced air induction could also be used if necessary, primary and secondary air could be separately regulated / tuned.
This rice husk gasifier is interesting, I don’t know what the internal design is, but he seems to have no issue with char burning to the bottom. However, rice char will be like a plug, charcoal might not behave the same at all.
Couldn’t find the video, but here’s one using the same concept. This one has a shorter combustion chamber, and a gate to open and close, that could be applicable.