Bain´s AA goup is the homologue from McKinsey´s AA or BCG Gamma.
They have existed as a small and almost back-office cell for a while, and approx. 3-4 years ago grew crazily and are a key part of the company.
They are also consultants, but with a much more analytical background (mathematicians, engenieers, physics, etc.). Their job describtion is also much more analytical, and they work in both usual engagaments or exclusively AA engagements -where there are usually also some generalist consultants, as translators, for instance-.
Their interviews, in line with their job description, emcompass not only the ussual business case + FIT but also technical tasks (e.g., related to data management, coding, etc.)
Hope it helps!