Cousin has a 825 that he uses for work with the USDA and puts roughly 3500 miles per yr on it now up to ~8500 total. He had to add good 6 ply tires on it (each year) and he did modify the air intake a bit but zero mechanical issues.
A friend in Colorado has one of the 570/590 smaller models and its been flawless with heavy back country use.
