They are territorial but no more so than any other fish with similar behavior. Chrysiptera are "typically" regarded has the more calm or well behaved. So Talbot's, Tracy's, Azures, Starcki, etc. Plenty of color, size, and action / speed. Again with most creatures in our glass boxes the onus is on the hobbyist to create an environment to limit the aggression and stock accordingly. Things to consider are rock work, nooks, crannies, caves, and things used for homes or territory. Food is another one by making sure they have a proper diet, enough food, especially if they are foragers. Of course there is also space.
Damsels have a bad reputation and/or image for many reasons such as used to cycle tanks, ignorance of their size, aggression, and habitat requirement. My own take is that this is true for any fish be it a tang or wrasse. Ignorance of size potential or feeding habits can take a otherwise common fish into a holy terror. For the record I've had breeding pairs of Azures and Talbots in a 40 breeder. I'm down to a single azure due to a mass rose bubble tip spawn a few years back but once the upgraded tank completes it cycle I'll be introducing more Azures, Talbots, and Starcki for sure. The color and movement is just amazing.
Note - I'm also probably a bit biased in that I've done some scuba diving over reef crests filled with these guys and gals.
