I was raised on the Clarke tinwhistle and have no experience with plastic mp types. However I've been given two of these (Ds) which I would like to use at a St.Patrick's Day gig.

The Walton's (Soodlum) is sweeter but way sharp on all notes. The Feadog is more in tune but not as clear.

Geraldine Cotter's tutor says of the plastic mp type "the mouthpiece is moveable so you can tune it to other instruments..."

The mouthpieces on the ones I have can't be moved by reasonable force. Should I get unreasonable or does Geraldine's statement apply to better quality instruments?