I used SPDs at first... couldn't stand the restrictive float. I can see how you had cramps with SPDs, NW. I switched to Speedplay X pedals. They are not even made anymore, but I see no reason to change to the newer version, as you can still get them. I kept SPDs on my mountain bike, which was dumb, since I already was scared to death and never really progressed much, flats would have helped. I had the campus pedals on my Jamis Coda; one side SPD, one side flat. They always flipped over to the unweighted side when I clipped out and I had to kick it over to get back in. However, I did ride that bike twice with the flat side and regular shoes, which was a disaster. In traffic, I had no muscle memory for pushing off unclipped. I have ridden beach cruisers/rental bikes with flat pedals, but with no pressure around me (cars) it was OK. I sold the Coda (wish I hadn't) when I got my Guru. That had Speedplay Frogs, which are great to walk in, but I always seemed to fly out of the left pedal. I read about it on line, there was an issue, mostly because it's so smooth clipping in, you can't hear the little click, so hence, you aren't actually in when you think you are. I bring them for when we go on tours in Europe. When we came back from Spain, we never put them back on the bike, and when I had to ride the Guru over the past month, DH put his old Speedplay Xs on the bike, since he bought the newer version, when he got new shoes.
I don't like change with any part of my bike! I don't have a good idea of how pins work. Do they stick into some kind of special bottom on a BMX shoe? If I ever get another bike like the Coda for just going into town, I might get flat pedals.