I use Look style pedals on my road bike but I don't think I would recommend them for fixed use. The shoes/cleats are extremely clunky and virtually impossible to walk in. Also, because of the way the clip mechanism works, I think you could potentially slide out the back if you were executing a skid. Again, I can't be sure because I haven't used them on fix, but it seem that since the opening mechanism is in the back of the pedal, it could be sketch

P.S.- I love them for road biking, though. They are the most comfortable pedal/shoe combo I have ever used because they offer a large flat surface/cleat for your shoe to press down on