I grew up in Norway, and have ridden dozens of Fjords. My lesson barn had about 30 Fjords, and most of my friends who later got horses got fjords (I of course, had to be different, and got a Morgan). There are high schools in Norway that specialize in horsemanship - many of them predominantly have Fjords for the students.
The Fjords aren't used in these programs just because they look cool or are a part of our heritage.
They are incredibly versatile. Some are more "drafty" and can be used for heavy farm-work. Others are more "sporty" and excel at jumping and dressage (they don't have the speed for cross-country). They make wonderfully sure-footed, level-headed pleasure and trail horses. They can carry a full-grown man no problem, despite their compact size.
I have been around very mellow ones, and quite spirited ones. They come in all flavors. Something for everyone. I would say they can all be quite stubborn, though. Friendly, smart, gentle, eager-to-please... but stubborn. They will test a rider to see what they can get away with.
There is a special way to trim the mane. One of the best instructions I've seen was on YouTube. I remember something from when I was a kid about finding the arc 1/3-way down the neck, etc etc... Trim the whole thing first, followed by the white hairs, then blending in the black center-section. Oh lordy, that was a long time ago. That mane is really thick and dense. Don't try ti until you've found the "instructions" and make sure everything is really sharp!