I have the ZL H51r, which is about 100 lumens of red light, and pretty awesome. It is also very easy to attach to the seat-stays or a rack with cable-ties. In the day time, on blinky mode, I know that cars are going to see me. (At night I switch to constant mode).
As much as I like my ZL, I must say that I think a slightly better bargain is the 2w Cygolight Hotshot. It's half the price, and puts out almost as much light. More blinky options. Plus, it has a nice internal battery that recharges off a mini-USB, and lasts longer than the AA's in my ZL.
I think a pair of those is a better use of 64 bucks than a single ZL. But both are great.