The mirror arrived in good time all the way from Germany. With my helmet - A Giro - the best attachment was on the INSIDE of the helmet on the RHS. I chose the Right side because this is my dominant eye. I think this is important. This position doesn't get in the way of my head as I thought it might. Follow the instructions carefully and the sticky pad works fine. They even provide you with a spare. They suggest that you try out the best position by using masking tape BEFORE using the glue pad. The pad can't be reused so check 2 or 3 times to make sure. The mirror gives a clear undistorted view. You can't see directly behind you because your head is in the way, but moving your head side to side to scan behind works fine. Try it on quiet roads first as it takes a little getting used to like anything new.
10 Months later 27/5/2013... I'm still happy with the mirror but the glue allows the mirror to slide around over time. I intend to use some epoxy resin to glue it better.