I do think that if BALPA's campaign is to be successful, their
PR department needs to make much more of the unspecified "management changes". You'd have to be stark raving bonkers to sign up to something that you don't know the specific details of. The fact that it is unspecified tells you all you need to know.
Where I work, any productivity-related pay deals involve specific agreements covering exactly what the changes are.
The general public at large seem to think that this is a "no strings attached" straight pay deal, which makes it look much more generous than it would appear to be.