As terrier21 has said the BRS-ABZ route was operated by Brymon, then by BACX. The route operated from at least the mid 1990s until summer 2002. The DH-300 flights were routed via NCL (as terrier pointed out), although they did try operating one rotation via MAN at one time but apparently it was not a success.
The frequency was at least three daily weekday rotations with a little less at weekends. For the route to have lasted so long, and it was really only dropped when BACX 'downsized', suggests there was and presumably is a market.
According to the BRS press release, "A survey of businesses in North-east Scotland late last year identified Bristol as the first new UK destination they wanted to see introduced at Aberdeen Airport."
There is actually a lot more to Bristol than aerospace and a port. It is a major financial and insurance centre and an important hi-tech centre of excellence. Add to this the fact that the Bristol area supplies 25% of the GDP of the whole southwest and there is the potential for business traffic. The Highlands also represent a very attractive tourist destination.
Given the right product at the right price Bristol has shown that it can support most services it has been given. Who would have thought for instance that 20,000 pax would fly each month between there and Newcastle? easyJet has shown that they will.
Eastern were reputedly going to start this service last October - there was a PPRuNe thread at the time. I have two slight reservations about the current initiative. One is the start-up in the winter when there will be few tourist pax and the second is the equipment. It is a long journey on a J 41. However, given the alternative modes of transport I guess most people would put up with a Jetstream.