I think that the new jet2holidays will help fill flights to places that might not be able to be filled with flights only such as LPA, SSH and Cyprus!
Altho jet2's 757s are not the best for comfort for transatlantic... are Globespans? or Thomas Cooks? who are all crossing the atlantic this summer from NCL with the 757.
I know for transatlantic the pax figure would have to be capped at about 200, but I doubt seats will be removed from the aircraft, but you never know the 757s could be fitted with extra legroom seats in the first 5 rows or so..
