I bought a set from Performance Bike a while ago (don't know if they still sell them). They worked well for a while, but the batteries died relatively quickly and were a pain to replace. Then one of them fell out while I was riding then the batteries in the other one died again then I decided they weren't worth the hassle. I have two rechargeable rear tail lights (one on the saddle and one on the left seat stay) and that seems to work well enough.