They are maintenance free so long as you don't get any foreign objects between the belt and the cog wheels like a small stone. When that happens, it destroys the belt or the cog wheel and then replacement is in order.
I look at belt drives as a manufacturing shortcut. Easy to apply in assembly, alignment not as critical and lower overall cost, especially compared to an enclosed final drive. The problem arises upon replacement. Major dissassembly is usually required simply because the belt in endless. You have a swingarm pivot in the way.
In my eyes, there is something disconcerting about depending on a rubba band for motivation. I'm into shaft (with it's equally disconcerting torque -climb the pinion-unless a Guzzi reaction) or chain, preferably 'O' ring variety.
One reason I bought the Rock was the final drive. Had it come with a belt, I probably would have passed.....Of course we do have output bearing problems.