The main problem with the Potters is, they have not been available for quite some time.I played the Killarney for a good while, but I now prefer a Potter.
It is an easy playing, quiet whistle, but the voicing (at least on mine) has squeezed it into such a narrow band tonally it is not a whistle I would use in a public setting.
Great for picking up tunes by playing along with recordings at home though. But overall, I'd feel the Killarney and the Potter have different uses.