Interesting approx fuel burn comparisons
Saab340 ~400kg/hr
Saab2000 ~ 900kg/hr
ERJ135 - 1100kg/hr
Obviously the fuel flow is only part of the economics with faster quicker flight times, full ownership and no repayments. I think maintenance costs of Saabs are also disproportionate.
BMI have done okay with them so dont think theres a major issue here. Im sure Loganair have 'done the math'