Simplicity,reliabilty,and feel.....own a redline SS mtb,its a big ugly heavy brute of a bike@32lbs,but it feels like its carved out of one big chunk of steel,very solid goes where you point it ride and almost bulletproof.If I break that bike it means Im prob dead from the accident LOL,thats why I ride SS.Once your used riding one hills actually become more fun I think,you stand up and pedal....and you get good at body english,brings the finesse vs brute strength back to the riding experience.I thought it would be a big handicap,it isnt,you can be faster on one gear than many gears if you know what your doing and your strong.I learned that on the trail trying to keep up with a group of guys riding them while I was riding a geared mtb......they dusted me w/o even breaking a sweat.They are also usually a tad lighter in the rear,makes bunnyhopping easier.Ive done 2 centuries on mine w/slicks,and ride it for work sometimes....they are pretty versatile.