I have the Airowear Airmesh and I love it. It’s basically the Outlyne but with more ventilation. It’s Beta 3 certified. I have a large chest and a long torso. All of the other vests I tried rode up in front (like a poor fitting turtle shell), interfered with my arm movement, or weren’t long enough. Airowear had the most customization options and my vest fits really well. I got measured in my local tack shop then they placed a custom order for my size. If your tack shop carries them (or any brand) that can be a really good way to get the sizing you need while also getting the support of a locally based shop.
Buy whatever fits you best. In my opinion it’s important to get a vest that has been certified, but many people ride in vests that aren’t. Personally, I like the assurance that my vest has been rigourously tested to meet a certain standard. I don’t really see the point of purchasing non-certified ones, but I’m not an expert.
I ride with my vest every single time I ride and you get used to it quickly. I feel naked when I ride without it in dressage tests.