My son had one about 6 years ago, but he was far enough along in his recovery it's hard for me to say how much of a difference it would have made. Basically he put it one, it inflated and then deflated kind of fast to shake the walls of their lungs and get the phlegm out. He'd often get a really productive kind of cough afterwards, more than he got from a CPT session (we did CPT for a couple of years) so it probably did work.
He called it his "shake vest" and thought it was super cool, though. He's always been a sensory seeker and to him this was the greatest thing. After we returned it (because he didn't need it) he'd still ask for it, so it definitely wasn't traumatic in any way. It was quiet enough that he could watch TV while doing it -- we did it in tandem with the nebulizer. One thing they told us is if you do it it needs to be on an empty stomach, just like CPT to keep it from making them throw up, or in my guy's case refluxing and aspirating.
If your insurance company covers it, I'd suggest giving it a try.