Indy, I'm so pleased to hear that you are sticking with flats. The marginal benefits that clipless pedals offer for technical mtb'ing just don't outweigh the risks in my mind.

I hope that the red pedals make you smile every time you look at them. One of the best things about cycling is decking out our bikes and bodies in really bold colors. Think of your red pedals as your alter ego outlet

I'll bet that you'll like your sticky-soled FiveTens on those pinned flats. The more flexible soles shouldn't be too noticeable since your flats have fairly large platforms to support your feet. My shoes also have pretty flexible soles. I haven't noticed any loss of power and the ability to walk comfortably is a bonus. But then again, having as much fun as possible is way more important to me than going fast