I used a home-made one for several years before I knew anyone actually manufactured one. I simply glued a small wide-angle mirror to a metal badge, then pinned the badge through the back of my glove. I thought it was the most clever idea ever, but the folks on these newsgroups hated it. Ultimately, I decided that a handlebar-mounted mirror was a better choice, overall. The amount of adjustability I lost was made up by the fact that I didn't have to take one hand off the bars in a tight, life-threatening situation.