I know a number of VERY experienced cyclists. They all use mirrors. But they all use DIFFERENT mirrors. There's no consistency in what is "best".
I tried one that glued to my helmet, it vibrated too much.
I tried one that clipped to my helmet, my helmet was tapered the wrong way where it needed to clip, so it wouldn't work.
I tried a couple of different ones that clip to glasses. I found one I like. Even with it, if you hit it while you're riding, you can knock it right off, so it takes an extra rubber band on it just to make sure that doesn't happen.
Anyway, sounds like maybe you're ready to try Mirror #2 now, so keep working on it and you'll find what's best for you.