I spent 5 years attending Penn State Behrend in Erie, PA. It was about 1.75 hours north of my parents house. Every time i;d get in the car to make the trip I would practice producing grunts and doe bleets with my mouth.
After practicing for a few trips to Erie I had it down, and the best thing is that no movement to put the call to your mouth or adjust to get a young or mature buck sound. Same goes for the doe bleet.
The only set-back and it is a major one, is that while in late season with any kind of scratchy throat or cough, I can't make the grunts or bleets sound good at all. also I tend to hack and cough and spook everything within a mile. Needless to say I don't try that anymore with any sign of a cold coming on.