I commute with mountain bike style SPD's all the time and have never fallen, or even come close.

My shoes are 6-6-1 sandals which work great for Spring/Summer/Fall and I have some Answer BMX shoes I wear on cold winter days (well, as cold as it gets out here).

You will be fine with them once you get used to clipping in and out (which doesn't take long).

Rick / OCRR