I've read that the new bottle dynamos are efficienter than the old ones. I put an ancient Miller bottle dynamo on the bike I loaned Alice. It is noisy, and the drag is perceptible, but the weight isn't perceptible when the dynamo is not engaged. The drag is not onerous, i.e. not like riding into a stiff headwind.

a bottle dynamo is a reasonably priced way to get dynamo lighting. It could be a gateway drug into hub dynamos for some people. Bike shops could -- and maybe should -- stock machine built dynamo wheels. They cost a heck of a lot less than building a wheel.