Underwear is a headache in my opinion. The changes are much less feasible, and the protection is seemingly less than a tabbed brief. I've always experienced leaks with pullups, and find them harder to keep up when saturated.
As for changes on the go, I've found most places I find the privacy of changing have 4-walls (unless it's a non-ADA stall). Even when there's not, I've mastered utilizing the toilet paper dispenser in lieu of a concrete/sound wall.
To me, the durability and comfort of diapers versus pull-ups are much more sustainable for anyone that requires dependancy exclusively to a pad without the ability to retain and find a loo once in a while. Plus added absorption.
It's all about finding the right product that suits your needs. I have bowel issues from time to time, and can't really go a week without an unexpected movement. Changing a brief is much easier to tackle and clean than underwear.