I ride clipless on my road bike.

But I personally would NEVER ride clipless on dirt. I hear too many tails of broken ankles with MTB because people can't unclip fast enough in an emergency, which there is more of due to the very unpredictable terrain of dirt/mountain. I'm clumsy enough with my road bike (20+ falls)
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2012 Specialized Amira Elite, upgraded carbon handle bars, Jett saddle 143mm switched to 145mm 2012 Selle Italia Max SLR Gel Flow saddle
2010 Santa Cruz Juliana with R kit and Crampon pedals
2011 Specialized Ariel Sport,suspension post,Serfas Rx Women's Microfiber saddle (sold)