Does the 24 hour opening have any relevance?
ABZ has been waiting for some decent competition for a while - even if the population isn't that large, there is plenty of money floating around, not to mention the distances either by land to other airports, or the simple fact that most other UK cities are not a realistic road or rail journey from ABZ.
I'm very surprised that it is or may be ZB, haven't we been awaiting a BE announcement for quite a while?
Both may pitch themselves at the quality end of the market, but assuming ZB would use A321s, they would have a lot more seats to fill than Flybe, assuming they started by basing a few Q400s there.