The ones that Shimano supplies with their pedals aren't intended for prolonged use. I understand that some people like having the option of toeclips or platforms with their clipless pedals and that's fine. For that type of application, I would recommend the Winwood InStep. You can get them for either Look or Shimano SPD style pedals. The SPD compatible InStep has mounting holes for two-bolt cleats so you can use them with other types of MTB style pedals than just Shimano SPDs.



For those looking for a pure platform solution, there's the Winwood Decksters. However, I think Decksters only come with SPD-compatible cleat mountings.



The difference between the above two pedal inserts and the one supplied by Shimano is that the temporary Shimano platforms are made with low-grade plastic formed into the shape of a cleat whereas the above inserts use an actual cleat bolted to the platform as you would bolt the cleat to a shoe. The Shimano platforms will quickly wear and degrade and are not intended to be ridden for more than a handful of rides. They are shipped with pedals as a convenience so that people can take the bike off the showroom floor at the LBS and go for a testride using any street shoe.