I have a Busy Buddy. I got it for my lesson horse who was fretting, sidling around, always shifting from one foot to another and otherwise being a pill when in the cross ties (28 yr. old set in his ways Appendix QH).
He got, uh, really expressive with his mouth the first time I used it. The second time I used it he was a little bit less expressive with his mouth. There has not been a third time because he stopped fussing in the cross ties except for an occasional “watch it lady” tiny movement.
When it was on him I talked with my riding teacher. Properly adjusted it went across his tongue approximately where the Weymouth curb of a double bridle goes when the mouthpiece of the bit is right above his curb groove. My riding teacher agreed with me when I wondered out loud if the two bits of the double bridle acted somewhat like the Bridle Busy Buddy when used on a bitted horse (I have not tried the Bridle Busy Buddy since I do not need it with this horse at all with the double bridle.) Previously I have had fussy horses calm down with the double bridle, could having a mouthpiece of a bit further down on their tongues be why they calmed down? Snaffle bit–fussy to super fussy (depending on the mouthpiece), double bridle–calmer mouth.
The Bridle Busy Buddy for use when riding with a bit is certainly MUCH cheaper than a double bridle. It may even escape being chewed on since the regular bit is closer to the horse’s molars.