When I ride my fell I do a running plait to keep his mane out of the way. I also use continental webbing reins as I found rubber reins snagged his mane.
One of my PREs doesn't grow a long thick mane for some reason (some say it's because he was gelded as a 3yo and the males stop growing a good mane after gelding?!). He looks quite smart with it short, though he's still fairly gangly and not that Spanish looking yet!
B was gelded at 18 months; on reflection I wish he had left to mature another year before backing. I think he needed more time to grow due to a lack of the usual iberian hormones. This might be reflected in the mane growth but on the plus side he has a great tail