score:9
The Practice of the Presence of God is one of a variety of different Christian "classics" which really cross denominational boundaries (Imitation of Christ might be another). Since the truths it discusses are universal to Christianity and because there is very little in the document which must be Catholic, its benefits are generally considered to far outweigh the detriments.
But, here is a counter question: if it is acceptable to read documents by other Protestant traditions/denominations, why is it unacceptable to read Catholic material as well? From the perspective of a devout Calvinist, Bonhoeffer got some things dead wrong, but he was recommended reading in my Presbyterian Church. C. S. Lewis is an Anglican, but you'll often see Baptists reading Mere Christianity. Chesterton is a Catholic, but Orthodoxy is one of the better apologetics texts in the English language. If all of these alternate theologians are acceptable, why is it unacceptable to read the writings of a humble monk on how to live one's life?