I love my dynamo powered lights. I have them on three of my bikes. I don't have to think about batteries or do anything to keep the lights working. Since dynamo-powered lights are normally bolted on, that makes them even more reliable than clamped on lights. There is a theft risk, but I've noticed that the thieves here in NYC don't steal bolted-on lights. I don't understand it, because it seems like an opportunity for them, but I have observed it.

I've been watching the systems that charge your gadgets from dynamo power. They don't seem practical to me unless you are going to ride long distances while away from power outlets. They are generally expensive, and the 5W or whatever it takes to charge a phone is really inexpensive when you take it from a wall outlet, so it is not a money saving system.

I run my lights day and night since the "cost" to do so is so low. It is robbing me of a few watts of kinetic energy, but I can't feel it, so it basically free. The benefit is that it might prevent a collision.