They run about $250 for a set of 3: 2 headlights and a taillight. That's more than most battery systems, but less than most dynamo systems not built in at the factory. And if you are really focused on high efficiency and light weight, whether for practical, aesthetic or obsessive reasons, Magnic Light is simply the best bicycle lighting system there is.
This concept could not previously have been realized practically because only recently have rare earth magnets become powerful enough, and LEDs efficient enough, for supply and demand to meet, so to speak. It turns out that any conductive material such as an aluminum rim - not just magnetic or ferrous - will produce so-called eddy currents when moving through a magnetic field. This invention harnesses these currents to turn a tiny generator without contact.
There are some issues. The biggest for people like us who use bikes to carry stuff is that since the lights and the generator units are integrated, they can be mounted only in locations that provide the correct small rim clearance and good light placement simultaneously. The provided mounting hardware doesn't have an answer for rear racks, whose mounted luggage will block the light. If you don't have either a skinny-tire fenderless road bike (Portland?!), or a bike with cantilever brake studs, there are only somewhat compromised mounting options. What's more there's no standlight, so you go dark when not moving. We'll make sure you understand all these issues before selling you a set: please bring your bike if at all possible.
We're pretty sure it's just a matter of time before the technology makes its way into more form factors, with broader feature sets. How about a stand-alone generator you connect to fork blade or seatstay that has power out for standard lights and other electronics? For now, for many, being an early adopter of the first, purest expression of the idea is part of the appeal.
What's wrong with cheap simple battery lights, anyway? No matter how much better they are than, say, 10 years ago, the inescapable reality is that the more you use them, and the brighter they are, the faster they burn out. The bigger the battery, the heavier and more fragile the light when dropped. Nobody would accept this dynamic in any other form of transportation. Battery lights are essentially disposables, at odds with the sustainable elegance of bicycles that can serve for decades.
What dynamo lights bring to the table, that battery lights never will, is liberty to run them IN THE DAYTIME. All the time, without a care in the world. With no bulbs to burn out and no resistance perceptible, why not? Tipped up just a bit, today's brighter LED lights are conspicuous a mile away in broad daylight! No battery light is bright enough to be useful in daytime without committing the user to a really onerous recharging scheme all the time. To my thinking, that's a better single safety investment than a wardrobe full of day-glo plastic garments and even a crash helmet for non-sport biking, because it can ward off rather than mitigate collisions. Our experience running bright daytime lights supports the conclusion of studies conducted with motorcycles, that they draw significant notice from other road users, preventing right-of-way violations in particular.
One last thing: one reason that battery operated lights have remained popular, apart from their lower initial expense, is that they can easily be transferred from bike to bike. If you care enough about safety and convenience to value the benefits of generator lighting, there's a good chance you own more than one bike. But then, equipping multiple bikes with generator lighting can be prohibitively expensive. Magnic Lights can be moved from one bike to another in seconds with no tools: only the inexpensive mounts need installation in advance.
One of the better early reviews: http://bike.duque.net/review-the-magnic-lights.htm