He accepted my decision- what are you afraid of?
He obviously hoped it would help, but if it didn’t, just go back to what works for you and return it.

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!