I have had CF my whole life (almost 19 yrs.), and have tried most of the different therapy devices and methods. I can tell you first hand that the vest holds a special place in my heart: there is absolutely NOTHING that I hate worse than that wretched device. Here are the problems that I have with it:
1) It is too LOUD. If I have to use that thing for 30+ mins., it could at least be quiet.
2) It is VERY HEAVY. CF patients are not very strong due to their lack of nutrition, and with the bad lungs on top of that, the vest becomes exhaustive to move.
3) In my opinion, it doesn't work very well to begin with. Maybe I don't have the pressure set at the right level, or maybe it's because the actual vest that I use is (way) too small for me, but it does not make me cough. Ususally the only way it will make me cough is because I have to move that machine.
4) Once again, this could be caused by the size that I have not being big enough, but it does indeed ride up terribly. I constantly have to pull it back down.
5) It doesn't help with the lower part of my lungs, although I think that IS from the size issue. (I never bothered to get a bigger size because I don't like it so much, and I am pretty noncompliant as well).
6) The bulb that you have to press can deflate through normal use. Also it is rather difficult to connect the bulb to the machine, it just doesn't ever seem to want to lock, although this might just be a problem with my particular machine.
All in all, even with the small size, there is absolutely nothing that I find advantageous with the vest over manual percussion.
As I said, I don't have the right size and I am noncompliant, but no one else has given you an answer so far, and I have used the vest. This is also a first hand account from an actual CF patient, so I do think that my opinion should have SOME bearing.
If you would like to talk to me further, you are welcome to email me: firstname.lastname@example.org
Personally, I would like to talk to you and hear your ideas on the subject.