While out bike shop hopping recently, it was brought to my attention that the Tubus rack I have installed on my bike has a light mount which is drilled to German legal standards for tail lights. I don't know what I was thinking, it's German. Of course they have a standard for that. Further more, there are lights available which are built to mount directly to the rack, and must also comply with the German standard for tail lights - during my Munich trip I did notice some pretty solid tail lights cruising around town. So rather than replace my tail light with another removable one, I decided to do as the Deutsch do and try out the light meant for my rack. Thus cometh the Busch & Muller 4D Toplight, which I ordered from Amazon.
On to the light itself. When I received the light, my first words were "JESUS that thing is huge." It really is. The lights themselves are two LEDs pointing in a clever triangular configuration, which makes the whole enormous thing glow like a big bug zapper.
Installation instructions are pretty much the same as any German product I've ever had the joy of installing. That is, they don't have nearly as many specifics as I would like. In this case, the back of the light is a solid piece of plastic and you're meant to punch out the pre-stamped plugs for the width of the mounts on your rack, a choice of 80 mm or 50 mm. I, not sure of what the IKEA-like instructions meant, punched out all 4 plugs. The light only comes with 2 bolts, which are apparently somewhat proprietary and not available from the bolt store. So I had to configure a new plug to keep moisture out of the light due to my own dumbness. Make sure to check which plugs you need to punch out, and only do those two.
Once I got the thing put together, installation was really straightforward - you pretty much put it where it goes and screw the nuts onto the bolt. Stealing it would require a very small hex wrench, so it's way more theft-proof than my prior lights.
As you can see here, this thing really is pretty gigantic - the rear of my rack is 120 mm wide and the light takes up ALL of that space. In 'Murican, that's about 5 inches. Per the German standard, it does not have a blinky mode. Your choices are "On," or "Off."
My morning commute starts before sunrise, so I had ample opportunity to assess it's effectiveness in the dark. I have to say, cars gave me a wider margin than I usually receive, and my theory here is that the size of the light, it's relative position on the bike, and fact it's not a blinky makes the cars relate to me something like a motorcycle or scooter. I took a lap around the block with a friend after dark and he reports that it is extremely visible from a couple blocks away and looks more like a car tail-light than a bike light, which corroborates with the behavior I've experienced with motorists so far.
For the brief week I've had it, I've been extremely pleased with it's performance, and at $35, it's priced right in the middle of other reasonably bright tail lights. I haven't seen it available in a physical bike shop, so it must be procured online, but it's pretty readily available from the internet. Two thumbs up overall.