all down to personal preference... i know BAR do a few.
Bisley, not so flexible, has a light leak right hand side, but i prefer it out of what's available as it accomodates different head positions in different shooting positions.
Pigs ear, very flexible, but perhaps too floppy... no longer made.
Cheap bellows version, very accomodating, but can allow the head to wander.
DG, very stiff, i find it not so accomodation as the Bisley as it doesn't allow me to shoot in different positions so easily.
But whatever one you choose, if they are setup right they should offer benefit over nothing, but I know several who just cant get on with them.