I have one nasty one (not totally evil though) and one that is only mildly aggressive. I have had very passive powder blues but I think that's less than 25% of them IME. Another 25% are moderately aggressive, the other 50% are varying degrees of aggressive that is more than most other tangs
Great fish, Acanthurus tangs in general are just a blast. My PBT is actually my frag tank fish and seems to really love the attention he gets from it and he loves getting hand fed. Ich can be avoided if you use proper quarantine procedures.
Ich in a 500 gal vs 55 gal is remedially different, only with most Acantharus tangs. It can be done to manage them with ich but you'll often kill dozens before you find one that hardy