I have both dynamo lights and battery lights on my commuter. The dynamo provides "minimum legal lights" and the Magic Shine clone (MSC), with a defuser lens, provides enough light to see by.

Tuesday this was useful. I hadn't charged my MSC for about a week and it gave up on the way to work. I still had a minimum legal light, provided by the dynamo, so I wasn't too concerned. Sure, in comparison it was just a dim glow; but I am more concerned with a ticket for no lights. I also, generally, leave the dynamo light on, so it provides a bit of a daytime running light.

Like I mentioned in other threads, the dynamo light takes a block or two to turn on; but that isn't a big deal. Even with dead batteries, the MSC will light for that long. It works for me; however, if I had to get ride of one of them (which I don't) The MSC is the one I would keep.