I will put money on its the supply boat crew swaps.
Vargar is the highest level of airport classification for training. Ie A cat C.
Which will mean that special training needs to be done every year for the pilots to be qualified to be allowed to operate into it.
Obviously a select few have been chosen to get this qualification to be able to operate into there.
It is a bit of a bitch to operate into, lots of turbulence, high ground and a long divert if they don't get in.
Eastern have operated into there before so its nothing new.
The boat company's used to use J31's for the route as well. But there aren't really any of them left these days in the UK. So the smallest cheapest thing left is the J41 or S350. And I suspect Logan air don't have any left for charters so its only the J41 left. Which to be honest is vastly more suitable for the route than the J31 which was only a minute shy of 60 mins single engine speed from Shetland.