Hey, thanks for giving some insight on different Protestants usage of the Our Father as a prayer.

Mainline Protestants seem to be quite close to the Catholics in using it, while the Evangelicals do not.
I do not hear anyone using it as a personal prayer though, which Catholics do very much.
As for saying that there is no sincerity in using it, well, that is obviously wrong. It is like saying there is no sincerity if you prepare your prayer, which is wrong too. If one talks to God, preparing on what to say, would not make the conversation insincere. In fact it would be more earnest, more important and you are serious about it, not wanting to say something silly and foolish but wanting to say out what you really think in your heart.
It does not mean to say that spontaneous prayer does not have its importance or that it would be silly or make mistake but more importantly that recited prayer may not be insincere. There is a saying that, ‘make the Lord ’s Prayer be my prayer too’, spoken from the bottom of my heart.