I have both the XFDD drum/generator hub and XFD drum hub, with the dynohub on my commuter bike and the bare drum hub on my touring bike.

Braking performance is excellent on both hubs, but only if you cut down the housing and cable to a shorter length than the provided prefab cable. Its so good that I don't see the point of caliper brakes any more in the front, even on a road bike. The hub only adds 400g, but lets you get rid of a brake caliper and use a lighter rim, all the while getting awesome all-weather braking.

The XFDD is the only dynohub I've used, and it works fine for that application, but drag is definitely there even when the light is off.

The XFD is the real star here, as it has simply amazing bearings. It has to be the smoothest hub I have used, and that includes all the best from Shimano and Campy.