I've used some sawtooth shaped rotors in the past, and they definitely didn't work as well as a "normal" rotor, mainly because they gave the brake a pulsed feeling at the lever, and didn't seem to be able to lock the wheels as easily.
That said there are a few different styles of Alligator rotor, and some of them look like they'd work better than others…
I'm keen to try the Ashima Airotor as I've heard good things about them, as in that they work just as well as a standard rotor, but are not much more than half the weight…