I have Shimano double-sided pedals. I ride with MTB shoes using the spd cleats 90+% of the time, but when I'm in heavy start n stop traffic, I'll ride the flats until the road opens up. I also ride the flats in street shoes for short errands or quick pleasure rides with the family, etc. If you do this, try to train yourself to use a heel first clip out motion every time you dismount, whether you are clipped in or not. Helps prevent embarassing moments when you forget if you are clipped in or not. I also found that multi-position cleats helped prevent clipout failures even in panic stops.
I understand platform pedals are supposed to put me at a disadvantage. Perhaps so, but I think in terms of power the difference is much less than is commonly supposed.
+1
While I like clipping in with my spds, during steady paces over relatively flat ground, I don't think they make any difference over riding the platforms. The only place I find them to be an advantage is in climbing and sprinting.