PG - I use one all the time now on my old boy - borrowed one off a friend first though as I didn't believe it.
Since using it he seeks the contact better and is far more laterally flexible than he was - previously he would flex then 'twang' back to where he came from as soon as any pressure left the rein - now he remains flexed.
I've got the velcro on one and put it on headcollar and leave him for half an hour before riding with it on (this is what the bumpf said and it does seem to make a difference) I then swap it onto the bridle - thake 5 secs
Edit to say ..... would try borrowing one first though to see if it works - I know 2 other people who use them and one had no difference at all (though she did want it to cure a headshaker) and the other had the same results as me
Have the Barnsby bridle with Magnetic Headpiece and it's work wonders of one of my TB's, she is more relaxed in her work and is working through her back nicely, would recommend it, but try and borrow one first..........
That was my point CS - mines Barnsby and I see a huge difference although others I know haven't - think it's definitely worth trying to borrow one first