A small Blue Devil damselfish and maroon clown were the first additions to my 75 gal. Since then I've added another maroon to make an almost mated pair (no eggs yet), a Yellow Tang, Lawnmower Blenny, Singapore Angelfish, Mandarin Dragonet & 3 Chromis, one of which is gone. In my naivity, I also attempted a Copperband Butterfly which starved.
At any rate, I really like the striking blue colour of the Blue Devil and it contrasts so well with that of the Yellow Tang. When I added the damsel and clown, they didn't harass each other too much since they were both small and about the same size. The original maroon clown is now the female of the pair and has grown to 3 times original size... the Blue Devil no longer comes near her, the male clown and their BTA! When I introduced the second maroon clown, not only did he have to deal with Clown 1, but he suffered lost a few shreds of fin to the Blue Devil. It was a stressfull month until the Clowns got along and the smaller one was safe in the Anemone with Clown 1. No mistake, the Blue Devil is a scrapper, but currently doesn't create too much havoc unless a Chromis or the Blenny get too close to what he considers his territory. The Tang and Angelfish have no problem with the Damsel since they are significantly larger, the Blue Devil discreetly gets out of their way. Another thing I find useful about the Blue Devil is that I've found him a good guage for feeding. He doesn't overeat, so I can sort of tell by his consumption as to whether I'm overfeeding the tank or not. The female Maroon Clown (Miss Piggy) is a voracious eater whereas the male is picky and seems to eat only Cyclop-Eeze granules.
Bottom line, I like my Blue Devil, he's got spunk & character, striking blue colour and hasn't been directly responsible for the demise of any other tank inhabitants.