I never really understood the "clipless peddles aren't safe" arguement. I was hooked from the first instant I tried it 15 years ago. I feel much safer and more connected to the bike with clipless. I use my legs and feet to manuver the bike as much as my arms and upper body. I have a real hard time riding on platforms. I feel like the only emergency manuver I can make on platforms is to bail.......that doesn't seem like a much safer option to me. I tried the dual purpose peddles on one of my older bikes and found that I never rode the open platform, ever, so there wasn't much point. If I am going to ride one of my bikes, I put on the appropriate shoes.

As for power and efficiency, imagine the transmission in your car only being half connected to the flywheel of the engine, and only being able to make use of every other revolution of the engine. Not very efficient. Work = Force x Distance. The energy used to propel you and the bike a given distance (Work) is the same, you are just spreading the force over an entire revolution (Distance) so half the force is needed.