I commute with traffic. I use one mirror at the left end of the handlebar. I tried it under the handlebar, but my wrist blocked the mirror and it was annoying to look around my own arm to view the mirror properly. I have it mounted above the handlebars now. With the mirror on the left, I can quickly view the traffic behind me. Being in the US, this is ok. If I were I. The UK, I would have it on the right only. I feel there is not a need for 2, unless you plan on weaving in and out of traffic. If I had an emoto like a surron, or many of the other clones, I would have 2 mirrors.