From the research I did before making the decision to try it, results are very mixed (there are plenty of anecdotes, but studies are few) [0] but it seems like as long as you try it on land first (on a non-diving day) to ensure no side effects, there's not much reason not to give it a go [1].
Doc says there's nothing wrong or clogged etc about my eustachian tubes. It's easy enough to manage (except skydiving, where the pressure change is too fast and not under any meaningful control of mine!), but if pseudoephedrine would make things less distracting during SCUBA, I'm interested.
Thanks for the links!
I use the generic (CVS brand) 12-hour extended release 120mg about an hour before diving, then two dives with a surface interval between, so I'm only relying on about 4 of those claimed 12 hours. I'm not sure the magnitude of the effect you warn of regarding accelerated processing, but there's a good margin to work with. There's also a 24hr formulation available.