I use flip-flop pedals on all my bikes. These are on my winterrainy day commuter bike. They are too heavy for a bike you want to go your fastest on, but they are totally solid and reliable for a utility bike. Clip inout is clean with easily adjustable tension.
I have had Shimano campus pedals on my mountain bike for years. When it was time to replace them, there was no question I would get another pair. When using road pedals on my road bike or two-sided SPDs on my single speed and commuting downtown, there are always the occasions when I need a fast start at a light and can't get clipped in quickly enough-you either slip out or fudge your way through. With the platform, you can do a couple of strokes on either side and clip in later. I tend to use this bike in lousy/snowy weather, and these pedals are perfect. (They also work great for actual mountain biking, though they do have a slightly larger profile than simple SPD pedals.)
I use these on mountains bike tours where I need to ride unclipped on my strong side so I can touch down immediately at tip-over speed on steep hills. The grip on my strong side (unclipped) is strong allowing me to inch along as required. Also, I like to use these at home when going to the gym or grocery store using my running shoes.
I have had these pedals on my favorite road bike for about 8 years and bought a second pair to put on another one of my bikes. Totally comfortable for use w/ street shoes, flip flops, boots, and if absolutely necessary, barefoot (not recommended though!). High quality, long lasting. Super useful. Highly recommended.
I ordered these as I have on more than one occassion hd folks that wanted to try out my recumbent trike but the pedals I had on it were clip on both sides. These fit the need that I had and are a quality product.
I put these on a friend's vintage Nishiki International road bike. He also has a MTB with clips. Now he can ride either with his shoes or hop on the road bike to run to the store. They are little heavy. I guess you have to trade off for versatility.