As usual, Irulan has very wise advice.

I tried out my husband's SPD that are built into flat pedals, Shimano M424, a few times. I even tried riding downhill unclipped on the flat part of the pedals because I know that I cannot unclip fast enough if I fall.

My "frozen with fear" body on the downhill switchbacks was not worth the 10% uphill improvement being clipped in.

Back to my beautiful Campon flat pedals I go.