I put dyno lights on one of my bikes last year, and I don't think I'm going back to battery lights except on my racing bike. I'm in the process of putting dyno lights on my other bikes. I like them much more than I thought I would, and I knew I would like them. I cannot perceive the extra drag at all. Maybe others can, but I challenge them to measure that carefully. The convenience of knowing they are going to work is fantastic. I can still mount a battery light if I'm concerned about a failure, but I've stopped doing that. The lights have proved very reliable. I get compliments on the beams they put out, too, which is pretty impressive for a 3W system.

The drag is so low (to me) that I run my lights in the daytime as well as the night. It might make me safer, and it might not, but it doesn't hurt to run them, as far as I can tell.

The drag from a sidewall generator is quite perceptible, so I only run one of those when I really need my lights.