Speedplay inverts the paradigm, putting the mechanism on the shoe and a simple "cleat" on the crank. The nice thing is it's two-sided. When comparing any pedal weight, it's a good idea to include the weight of the cleats to get a more complete picture.

Out of the types of pedal systems I've had or tried, Look, Speedplay, Eggbeaters, and SPDs, I prefer SPDs. Their downside is few good road shoes that take the cleats are available, and walking on them is bad except on mtb or touring shoes where they are recessed. If the sole of of the shoe is stiff, the size of the pedal platform is irrelevant, IMO.