This is a great attachment for the Take A Look Mirror, which is the best bike mirror on the market. I am a heavy-duty rider (commute and many, many weekend miles) and would never ride without my mirror. The key, though, is how you attach it to your helmet. Forget gluing this thing to the outside of your helmet with those little sticky pads, I completely agree with the one-star review as to that method - it is not great. What you need to do is cut a small slit at the bottom of the hard-foam padding on the inside of the helmet shell to tightly fit the top tabs, and slip the top tabs up into the slit. Figure out the optimal placement of the mirror, and make the cut. A boxcutter or very small Dremel bit would work. (Remember, you can always make the cut bigger if needed, but once done, you can't make it smaller, so be judicious.) This is great way to attach this mirror - FAR better than attaching to your glasses, the angle is better, the mirror is completely stable, and, additionally, on those long steep climbs you can pull off your fogged glasses and continue to use your mirror. I have had my mirror mounted this way for years, with nary a problem, it does not come out (and, trust me, on these pothole Sonoma back roads, if that was an issue, I would have discovered it). In fact, the only issue I have had is that I have used it so long, the plastic is becoming a bit weak from wear, and thus I am replacing this little plastic piece (my mirror is still going strong).
I did not like the mirrors that attached to the outside of my helmet; they were small and limited my rear view of the road. This is better and with the Take a Look mirror being so easy to customize your view you can get a much wider rear view and see more of the road. It takes a while to get the mirror setting right but when you do you will not want to go back to the small oval mirrors because of their limited view.
Worth the small cost IF you like to use a mirror without having to attach it to you glasses. It's really tough plastic that can be bent to fit the contours of your helmet without breaking. The provided adhesive isn't that strong, however and I yanked it off by accident.
I have a Bell Lumen helmet and this adapter put the mirror much to close to my eyes than just having it attach to glasses. Also w this adapter you have to attach the mirror from bottom up which makes the overall position of the mirror different than attaching it on my glasses from the top. I much prefer the view when it's attached from the top. I tossed it after failing to find a good work around. Good thing it only cost a few bucks. I'd just use the mirror on the glasses and pass on this.