Hi Kate,
You sound just like me! I am thinking the very same thing about the vest. I neb with 7% every day and do the Aerobika simultaneously. That combo is quite effective in bringing up the gunk. But...the vest, which I use following my neb session brings absolutely nothing up! I keep thinking I should return it. But then I am apprehensive, thinking maybe, on some level it is helping and better to have than not. (?!) This is a dilemma I've been dealing with for quite a few months.