i’m pritty sure it can accomodate B737 and A320 size, bmi uses A320 on the LHR run. There has also been several B757 movements, but in the main by very lightly loaded government/VIP examples
i have to say i really do prefer the 5 point harnesses over the cabin lap belts. even with a 5 pointer without the soulder restraints just felt a lot safer in my eyes