I've been fixed gear MTBing for many years on an old 26er Redline Monocog. I don't know anyone else willing to try it. And people I ride with are blown away how I can maneuver fast through winding narrow trails without coasting, although its not really that difficult if you are an experienced fixed gear rider. The lower gearing of a mtb gives you a lot more control than a typically geared road fixed gear, which helps navigate tight, winding, twisty, hilly trails. Riding fixed changes the whole feel of the trail. The difference between riding the same trail fixed and SS is almost the same as riding two trails. Although, honestly, trails with log piles and other technical interuptions just make it tedious. I can manage these things, but having to skid and skip around to prevent pedal strikes gets annoying after awhile. Flowy, winding trails I ride fixed. Techy slow trails I ride SS. Trails with fast gnarly hills and steep long climbs I go geared. Pick the appropriate tool for the job.