Cityjet out of Belfast was a flop because of the skyhigh prices. 328s are great little machines to fly on as a passenger, but not good if you want to appeal to the mass markets in terms of price.
By comparison, having used BA Cityflyer, and even Cityjet on the Avros out of Dublin, prices tend to be lower. I hope the new Flybe routes work well, my only concern would be an 8.35am arrival at LCY cuts it a little tight to make it for a typical 9am meeting in London