That's kinda my point. It is one thing to stick the in-line octo in your mouth now and then and get used to the exchange and to breathing it, it is quite another to use it while ascending, especially if the person using your primary is on the edge of panic, which would not be unusual.
The integrated-with-inflator octos usually have a bump halfway up the corrugated hose, which is attached to the cord inside to dump at the left shoulder. But the add-on in-line inflators like the Shadow and the Airwave have two ;problems: (1) no easy way to dump, so you can go for the task loading as you describe (if you don't have a right-shoulder dump, and (2) they do not have the large-diameter hose feeding them like the integrated units, so the air-flow is restricted, and you can't breath hard and fast and deep from them. All in all, I think they are dangerous rather than desirable.