Hi, I don't use one myself being a couple of tennis balls and a whistle type trainer these days. If you are in the UK this week's Shooting Times magazine has an article reviewing training vests.
In life, it is important to know when to stop arguing with people and simply let them be wrong.
I use a vest when out on lessons etc, mine is a pinewood brand. The one thing I’d say about wearing a vest, is sometimes the items you’re looking for within the back pocket do seem to get “lost” a lot! so less is more I’ve found.
Much as I like vests, I find now I have to consider wether I can use the rear pocket ok.... years of abuse and lifting silly weights means that arthritis effects both shoulders. hence I have a Mystique one that I prefer but also have game bag or carriers in the landy for if they are playing up.