I love the passoa system and have used it to great effect on a young horse wgho needed to learn not to panic in the transition to canter and to balance himself properly. It enabled us to hang on to him when he paniced
this is him relaxing in the passoa PB040133 - YouTube PB040132 - YouTube
This is him panicing (so you can see why we couldnt hold him PB040134 - YouTube
Not everlyone has the skill to use double longreins and the passoa takes away the error from it.
The Passoa does not Force anything, it encourages but if the horse wants to trail along with its hocks out then it can
Hock hobbles have no give in them, thus you are essentialy tieing the mouth down and to the back legs and the horse gets hit in the mouth hard every time the hock goea back.
The aim of the passoa is not to force the head down at all, the triangluar nature of the passoa prevents the horse being hit in the mouth (if used correctly) and a horse can easily and safely move its head up and down and stretch into a contact.
I've met top dressage trainers who love passoas for young horses
To answer the OP no it wouldnt work on a noseband as it is designed to engage the hocks and encourage a horse to stretch into a contact without getting socked in the mouth you cannot strtch into a contact unless you have one in the first place and you cant have one in a halter