I've been using a XL-FDD dyno and XL-RD5w for 6000 miles. Extra weight acceleration is slower for sure, but overall probably BETTER. I would say the dyno drag is the same as a mechanical speedometer, a little 1% speck. I've done 45 mph on this 9%/300 yard hill every time. My theory is the mag lev effect at least helps reduce bearing load. My Edelux light is always on. It is far brighter than the old bulbs I had which I used at first with the new dyno, until they burned out.

The bottle generator I had long ago on the other hand sucked 25% of my speed and 99 % coasting at least. Going 20 mph was impossible and reduces tire life likely 90%. They were horrible to even adjust them to work at all.

There is no free lunch with those horrible rechargable batteries either. They go dead in a week or 2 with zero use, wtf ?
Using them with anything but these low load leds is hopeless. Fried Teslas, Dreamliners anyone ??
They are 1.25 volts instead of 1.5, wth ?? Does EverReady,etc have a Patent on 1.5v ??

11 years ago my bike's LBS came out with those 1/2 litre/3 lb pig batteries and the LBS owner couldn't understand why he should even offer dyno hubs for sale ?? WTF. Besides that they would maybe last the whole night ?? LAUGHABLY STUPID !!!!!!!