Yeah, I have that light. I got it because, at the time, it was the only light I could get my hands on (as in look/feel in store vs. online) that seemed appropriate in size to be mounted on a rear rack. I have a tubus rack that it's mounted on, and it comes with all the hardware you'd need for rack or post mounting. Overall I am happy with it. When I first got it...it frustrated the hell out of me. They have an "auto-on" and a standard version of this light. I got the "auto-on" version and it has a light sensor which, for me, does not turn on soon enough. I like the light to be on if it's raining/foggy, but if it's daytime usually there's still enough light out that the light won't trigger on. Even near the sunrise/sunset hours when you'd like to have it on, the sensor doesn't seem to turn the light on until it's pretty dark out. To remedy this, I opened the case and put some electrical tape over the light sensor. Now it just turns on/off when I push the button instead of waiting for it to get dark enough. In hindsight I would've just gotten the non "auto-on" model. The auto on feature, in my opinion, would be great if it the light sensor were a bit more...sensitive. In terms of brightness I have read some reviews that some people are not satisfied with the light output. I'll admit that it's certainly not the brightest rear light you can buy (PB Superflash is easily brighter), but as a rack light it fits the bill and I really like that it doubles as a large reflector when it's not turned on. I parked my bike about a quarter mile down a bike path near my home one night just to get an idea of how bright it really looks at a distance; for me it's plenty good enough. I haven't used the 4D so I can't compare it but a friend of mine has the 4D and just looking at it, I feel light the Cateye is brighter, also it has cool flash patterns.

Bottom line, I do like the Cateye light but if I were to buy all over again I'd just get the non "auto-on" model.