Which flat pedals and what shoes?
I ride these with no problems on my commuter, they do slip a bit when wet. The solution on this is to drill and tap some of the round protrubrences and add some set screws. I haven't gotten around to doing that yet.
A maybe better solution are the Thin Gripsters which are pretty sticky. I've used these on my gravel grinder, they work very well.
The main feature of both of these pedals vs most others is the significantly larger surface area. This allows you to wear a "soft" shoe and not hurt your foot from force concentration on just the ball of your foot.