I had SPD platforms on my 4300 for a while. The way I rode, I hated it. I don't even know why I did it, because I don't even have the shoes for them. If you have the shoes, then it's worth it, but I spent all my time trying to flip the platform upright when taking off and it drove me nuts.

That said, I'll probably put them on a road bike when I get one since I plan to go with clippy shoes and would also like to be able to ride without them