I have the AD600 and love it. It's not too loud, is easy to set up and clean and skims like crazy. I have nothing bad to say about it at all, best skimmer I've ever owned.
i have it for a week now. absolutely fantastic... i had before bubble magus c7, deltec 600ix and nyos 120. that are all toys when comparing to ad600. silent, started skimming in 1 hour.