The choice of aircraft was limited by the runway at Alderney. Viable options on performance were Dornier 228, Twotter, LET410 and Trislander.
The most flexible for a mix of passengers, medevac and freight is the Trislander which has been doing the job for 40 years.
Dornier chosen partly because when cross wind performance looked at it appears Aurigny management can't tell the difference between demonstrated and actual performance limit.
Trislander ruled out because it doesn't look like an airliner, despite the fact they could have bought 5 brand new ones for the price of a Dornier and B-N were willing to build them on that basis. Moreover it has taken longer to get the Dorniers into service than it would have to build the Trislanders.