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This purchase was a gamble because I really wasn't interested in what I feared would be extra drag and weight just to power a headlight that I might rarely use. But because I go on occasional bike/camping treks, my hope was that I could get the dynamos' output to charge AAA and AA batteries which I could then use to operate a flash light, tent light, reading light, mp3player/radio, etc., in addition to the bike's running lights. The charger I intended to use (UltraLast Green 2AA/AAA/USB On-the-Go Charger with 2 AA Everyday Precharged Batteries) supposedly can also power cell phones through one of its adapters.
After receiving the hub dynamo (ahead of schedule from Bikewagon), I purchased 4 silicon diodes and a USB cable from Radio Shack and built a bridge rectifier to convert the dynamo's AC output to DC required for the battery charger. Because the dynamo output was approximately the same magnitude as the charger input requirements, I was somewhat optimistic for the big test, but guessed it would take at least 3 hours to fully charge 2 completely dead AAA batteries. However, on the test ride I checked the charging progress after 1 hour of pedaling, using a separate battery level indicator, and to my great surprise found the batteries completely charged!
As far as extra weight or drag, I haven't been able to detect any, although I should qualify this by stating that I am a coaster-brake bicycle aficionado and not obsessed with speed. In addition to the dynamo, I believe the Sturmy Archer hub is the only one with a drum brake, which like a coaster brake is protected from the elements. The drum brake has worked out just fine for me as a standalone brake, or in conjunction with the coaster brake to reduce the heat stress of long steep descents. It is comforting to know that the drum brake is always there if the chain derails and the coaster brake becomes useless.
I do have one minor complaint about purchasing the brake lever. The dynamo product description did not state whether the lever was included with the package, although the "frequently bought together" line implied that it was not. I took a chance that it was included and ended up purchasing the lever separately which cost me some time and extra shipping costs. But having a quality alternate brake and being able to generate all the electricity I need for my traveling devices more than compensates, as does the great customer service I received from Sturmey Archer (North America) regarding questions I had about the hub. I greatly recommend this product.
CHARGING UPDATE May 26, 2012: the performance of the above described charging system has declined over the past month. I first noticed that the charger's output function was not working and now, after a few hours of pedaling, dead batteries barely get over half-charged. I am pretty certain there is not a problem with the Dynamo, because the same thing happens when I use the charger's AC adaptor to charge batteries. I certainly can't fault the charger either, because charging it with the variable output characterized by the dynamo is not listed as a feature. Thus the problem could stem from my lack of circuitry knowledge, or even from inadvertently attempting to charge batteries inserted backwards for a short time. At any rate, the initial success showed me what is possible, which will keep me trying (and learning).
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I like this hub a lot, particularly for my previous, 10 mile, unlit bike path commute (with Busch & Muller Cyo light also excellent).
Braking: could be better. When new it's pretty bad, but gets better over the next couple of hundred miles. Better than an old single-pivot caliper, not really as good as a modern dual-pivot, let alone cantis, linear pull, disks. Still, quite adequate mostly. Not *entirely* maintenance free eventually get dirty and water does get in there, at which point braking is not as good and they can even stick on. At worst I had them lock on, when very dirty. Cleaning isn't too onerous, and typically once every 3-5k miles. Braking is quite bad the morning after a wet ride home, as some sort of grime has to be dealt with.
Drag: quite apparent when spinning the wheel, not apparent with > 200lb momentum. The bike glides along nicely. It'd be nice if drag was lower, but for the typical
