I have done quite a bit of traveling with my vest and nebulizer, and I hate to say it but it can be frustrating. Technically, the vest shouldn't count as one of your 2 carry on bags (as it is medical equipment) but airline employees oftentimes, a) don't believe me, or b) aren't familiar with this regulation (?). When you check in, you may be asked to check your "extra" bag (vest), so I usually try to explain ahead of time that I'm traveling with medical equipment, although sometimes this just makes it a bigger deal than necessary. The actual security has always been very understanding. You will have to do extra screening for the vest (sometimes the nebulizer). I usually try to plan for a little extra time, because I know it'll take a bit longer as they have to run the machine through again, ask you what it's for, test for explosives, etc. I think these staff members are usually pretty understanding because they see all sorts of medical devices coming through, at least that's what one told me once (i.e pacemakers, oxygen, etc.). When you board your flight, you may be asked about your bag again, as well as when you're actually on the plane, sometimes a flight attendant will try to swoop in and tell me I have one too many bags. However, once you get it in the overhead compartment (sometimes a nice guy or lady will help you hoist it in there!) you are done with dealing with the questions and the bother of flying with your machine!
What I have noticed, is that airports outside of the United States are very understanding, and I've never run into any problems (except once in Brazil trying to explain what my nebulizer was to a security personnel and another time getting home and realizing they had confiscated vials of pulmozyme and hypertonic in Turks and Caicos!). The contrast was very apparent flying from Buenos Aires to Newark - the people in BSAS airport were wonderful, very understanding about my medical equipment (didn't make a big deal out of it whatsoever). Almost immediately upon landing in Newark I was (not to sound dramatic) harassed for my "extra" bag as I was entering the line for security. When I explained that it was medical equipment, the lady rolled her eyes and called over another staff member, and told her I was "claiming" (she actually used quotations) that I had medical equipment. She ended up letting me through, and as I continued in the line, there were a few people who asked me if I really did have medical equipment...! It's interesting-- when I fly alone or with a friend, I am more likely to run into troubles, however, if I'm with my mom (I'm 21) it is pretty much smooth sailing. Not sure why this is, but I assume I'm just taken a bit more seriously with my mom there.
Has anyone else experienced problems? I strongly believe the airlines need to make some changes in regards to the treatment of those carrying medical equipment because if I (and others) have frequently experienced issues, I would imagine we are not the only subset of those traveling with medical devices who are treated poorly.
Don't let this deter you from traveling, though! You will be able to travel with it, and if you run into problems, just calmly explain the device, etc. and have confidence in the fact that, legally, you are able to fly with your vest!