I went from platform pedals to toe clips then on to SPD clipless.

I used toe cages with the straps loose and never had a problem. I still use toeclips occasionally on a commuter bike.

When I went clipless I made sure the tension on the pedals was very loose, I still use them this way. It's easy to unclip, but I have never had them unclip when I didn't want to. I fell once or twice when I first got them. Climbing was a bit scary at first as I could not coast to unclip, but I do fine now and can unclip while pedaling to stop on a hill. If I'm in a rough spot I can unclip one side and just put my foot on the pedal while pedaling if I feel I might need to stop.

My mtn bike is not clipless yet, but I am ready to go clipless on it soon. I have half clips on it, just a little little plastic part that slips over the toe of my shoe and keeps my foot from going off the front of the pedal. These have worked ok, but are sometimes tricky to flip over the pedal and get into while going down a rough spot.

I have a pair of the Nashbar SPD pedals, $20 on sale, on the way to try on the mtn bike and I am going to try the "chicken cleats" that come unclipped very easily.