My only experience is with the adapters that come on new bikes from the LBS. They were no good for anything but a test ride.

I ride my 14X2 commute on a single speed. I have a pair of the Shimano M324 SPD/Platform pedals (metal cages). I find them very convenient especially when having to get started across an intersection on an incline, If I miss the cleat, I can alway get the platform side and get across without stalling, and irritating the motorists behind me.

The natural hang of the pedals favors the clip side with the natural starting motion coming from behind the pedal and rolling it forward. If I am in regular street shoes I roll the pedal back from the front to get the platform side. It's really pretty easy (if I explained it clearly).