Dr.s Bruce Haskill and John Mink featured the Bluegrass appliance in their article published in the Journal of Pediatric Dentistry, Volume 13, number 2.

Patients with thumb-sucking habits find it easier to tolerate than the rake-type habit appliances and have a greater success of breaking their habit because of the roller giving the
tongue something to play with, therefore eliminating the need for the thumb.

This is best suited for mixed-dentition cases.