They are definitely character fish. I love them in my tank. Unfortunately in a 400g tank with lots of rock there are so many places these little guys vanish to.
Then one day you are feeding and that little head shoots out of the rock.
I will say when I have seen these in quantities at the wholesalers, they are very aggressive to each other when in the tanks.
I have found that they are definitely territorial, but they seem to badger each other to spread themselves around the tank and settle in.
Dave B