Quite honestly, I think statistics can show some important things, but there are people who like the vest and people who hate it.
If you love it, they you are going to use it regularly and it is productive for you. If you hate it, chances are you won't use it and then it becomes pointless and maybe even detrimental to your health because others "assume" you are doing your chest PT with the vest and don't think you need the manual anymore.
The huge benefits to it are that it takes less time to do the vest than manual chest PT. My husband was prescribed 1hr chest PT in the AM and 1 hr chest PT in the PM. That required time out of both of our busy schedules and required me or someone in the family who knows how to do chest PT-to be home.
With the vest, he does 20 minutes in the AM and 20 minutes in the PM and NOBOBY has to be home to help him. IT's really beneficial to us. He can still watch TV (and recently he's even mastered doing his homework while doing the vest, but don't ask me to read anything he's written because it doesn't make sense-scribbly all over the page) or do some other sedentary tasks while he is doing it. With manual Chest PT, all he could do was lay there for the PT.
If you are a person who dislikes the vest though, and many do, all those things I mentioned are pointless because you will dread doing it and likely not comply and not do it.
There are studies going on right now by accredited CF centers and some independent CF doctors/pulmonologists for the Vest. Mark was going to be part of it but they had already ordered his vest (he hadn't recieved it yet, mind you) so he couldn't qualify. But I assure you, there are independent studies ongoing and coming out right now.