Be Your Own Advocate and tell your Doc it didn't work for you. My Pulm says it is an "option" some people like. I tried it under a 30 day trial period and took it back after a week. Like you, I can do my own postural drainage and felt the vest wasn't bringing up any more than I could do myself. I also was not able to nebulize as deeply because the vest constricted my airways. The Vests are expensive! I bought a small $50 percussion shoulder wrap and use it on my lungs - it works pretty good! My guess is your doctor won't have any problem with you not wanting it.
Good Luck!