I have the Blackburn Flea 2.0 USB lights, both front and rear. They are mounted on my Bell Muni helmet. For what they are, I think they're excellent lights. I wouldn't be using the lights as my only lights for night use, but for your use, I think the fleas sound like a great fit.

The lights do not fit directly into a USB port. A small dongle is provided, that fits into a USB port. The Fleas attach to the dongle. I purposely bought my front and rear Flea lights separately, to make sure that I got two dongles. One dongle is used at home. The other stays at work. As a bonus, one light also included a solar charger. I am currently working on a way to attach the charger to my backpack, so I can charge my Fleas as i ride in the sunshine.