Unsafe bike riders are a pet peeve of mine. I leave for work early in the morning, when it's still dark out. Every day I drive past at least the same three bike riders, who depend solely on those little reflectors on their peddals to help me see them. They have dark bikes and wear dark clothes with dark backpacks.

They are riding on the side of a busy road. No sidewalk. No bike lane. One or two lanes of traffic going each way, and surprisingly busy at that time of the morning. It seems inexcusably careless to me.

A device like the OP shows, or some of the others mentioned by other posters, would be a welcome addition in my mind. A light coloured jacket, backpack or a reflective vest would even be an improvement!