I rode pedals like that for awhile (years ago). At least on the ones I had, the platform stays up, the cleated side down. So when you are riding with your SPD shoes you need to use your toe or something to flip the pedal before you can clip in. It's not difficult, but it takes a little extra time.

Originally I was riding primarily on the SPD side, so it got annoying having to flip all the time. Then I was in a phase where I was always on the platform side, so it wasn't a big problem but at the same time didn't provide any benefit having the SPD. If you are using both sides on a regular basis I can imagine it being nice, but I never seemed to be doing that.