I have been training with a fixed-gear for a couple years. For climbing hills, it was very good for me. I love hill workouts on my fixie. For cycling in general, I don't think it has been good for me. It has made me develop a lower cadence, because it's a big gear, and it has made my pedal stroke lazy. The laziness comes from the fact that the cranks move my feet for me. I think a fixie will only help your pedal stroke if it's a relatively easy gear. Otherwise the bike takes over.