After nine months with the dynamo hub, I still love it. It adds weight and resistance that a removable battery light wouldn't, but you would have to remove the battery light to save the weight. So that just leaves resistance.
A transportation bike is going to weigh more than a sport or competition bike. Even mountain bikes are using exotic materials and evolved designs to reduce their weight compared to bikes with similar features from a decade or more ago. But the transportation category includes cargo bikes and heavy tourers, so we quit worrying excessively about every gram when we started down that path. Or road.
In 1980, when I worked at my first bike shop job and thought it was a temporary thing while I got a more illustrious career in order, our tribal elder and wise man -- he was 32 -- told us that a generator adds about a gear's worth of resistance when it is operating. He said this as he was installing the classic Union bottle generator onto the Motobecane he was configuring as a fixed-gear commuter with racks and fenders. We were all assembling different forms of the same thing. Most of us, with limited budgets and more of a focus on racing, used completely inadequate lights.
When I got a better job (relatively speaking) the following year, I invested in my own Union generator, and later acquired a Sanyo that drove off the tread face of the rear tire, rather than the sidewall. The increase in resistance never seemed as clear-cut as "a gear's worth." Does that mean a one-tooth jump or a larger increment? Even in the days of anemic incandescent bulbs it was great to have a fairly steady light. With Union's battery pack accessory it would even stay lit when the bike stopped. Any resistance it might have added was never enough to discourage me from flipping the lever to activate the light.
The specter of resistance still haunted me. When I moved to my present home and faced a 14- to 15-mile hilly ride each way for my commute I carried as little as possible on the bike or myself. The season of darkness ended my riding each year.
When powerful battery lights emerged as mountain bikers pushed into the darkness, they offered amazing illumination compared to any battery or generator light I had previously encountered. But then the problem of battery life became more important. When your light is already pretty feeble, its dimming seems less dramatic than when you start out with something that lets you read a newspaper at 50 yards when it's fresh, but leaves you groping in its dying glow when the charge runs out.
Rechargeable batteries needed careful handling to avoid over-discharging them and over charging them. As battery and charger technology evolved, we were told that running the batteries out was no longer a problem. So-called smart chargers eliminated the problem of frying the batteries if you left them baking too long as well. After using some of them I remain unconvinced, especially about the chargers.
At best, rechargeable batteries have a finite life anyway. They can only survive a certain number of charging cycles. So you go through a period of diminishing efficiency as the battery nears the end of its functional life.
Cold temperatures also diminish the power of many batteries. When I used my mountain biking light as a headlamp for night skiing I had to tuck the battery inside my clothing. When I took cold rides with the battery mounted to the bike it would suffer from the exposure. The battery lights I have on my helmet now don't work as well in sub-freezing temperatures. But then, who does?
The SRAM iLight hub dynamo I chose had very few reviews on the Internet compared to the Shimano, Sanyo and Schmidt hubs. Schmidt is the gold standard: expensive but excellent. Shimano is often rated as the next best choice. Shimano has prospered for decades making the second best item in many categories, bringing them to market at a price significantly lower than the top brand. Now they are recognized as a leader by many. Love 'em or loathe 'em, they do put out a lot of useful items along with container ship loads of technofascist whizbang garbage. I try to avoid them when I can because of that, but they're so huge that they end up providing things their major competitors won't.
Shimano made my job easier when choosing a hub because they did not offer a 36-hole hub that was not set up for disc brakes. SRAM did. So did Schmidt, but I work in a bike shop. I'm not pulling in Schmidt money. We have an account with Peter White, importer and distributor, but even with that it's an investment.
The SRAM seemed like it was a bit better than the Sanyo for comparable money. In particular it seemed to have lower drag with the light off. That resistance is the price you pay for unlimited light.
A 36-hole hub is probably overkill for my commuting routine. I went with something that strong in case I take a heavily loaded tour. Since I can imagine putting dynamo lighting on almost every bike I own now, I could see building on hubs with lower spoke counts for some of them.
Because I have not ridden with the Schmidt or Shimano hubs, I can't say if I would find them easier to push. The Schmidt certainly has impressive numbers, especially with the light turned off. However, I don't go without the advantages of the dynamo hub just because I could not afford the very best.
If you have a frame with a dynamo bracket already built onto the stays or fork, you can mount a sidewall generator like the Busch and Muller Dymotec 6 I used initially. I had problems maintaining alignment because of the tires I use and the way the add-on mounting bracket clamps the seat stay. Rather than continue to put a hurt on the frame tubing I went to the hub. With the sidewall generator you have zero resistance with the lights off. The downside is that you have to make specific arrangements to improve performance in wet weather. The wire-brush roller for wet conditions can mess up a tire pretty quickly if you don't have it lined up right. Also, most tires do not have a real dynamo track molded into the sidewall. German brands are more likely to, because of Germany's lighting requirements for transportation bikes. It's not a feature most tire makers highlight in their product descriptions in North America.
If you go with a dynamo instead of battery system you can get accessories to charge and power your small electronic devices so the electricity you produce during daylight won't go to waste. Some lights also come with daytime running lights now.
I have noticed that motorists show more respect when I run the big light. Something about its power seems to put me on a more equal footing. Fewer oncoming drivers leave their high beams on when I have a light that makes a bigger impact on them. It's aimed down where I need it, so it does not blind anyone driving toward me, but it clearly gets their attention even when I'm not running flashing lights on the handlebar to enhance visibility.
The wide Toplight Line Plus tail light probably helps for overtaking vehicles, but I never ride on the road without my full array of flashing tail lights as well. The Planet Bike Superflash pounds out a sharp warning that commands respect even when the sun is up. As the centerpiece of a night array with two flanking flashers it probably makes me look like an official vehicle. The bluish tint to the Beamers in flashing mode on the front of the bike may subliminally suggest police lights to drivers who chronically have a guilty conscience anyway.