Our job is to learn our own faith first, and only then to examine the faith of others. Know that Luther’s teaching was, in many cases, distinctly Catholic in nature, since he was a Catholic priest and theologian. However, once Luther rejected Church leadership in favor of his own leadership, teachings quickly morphed into the directions of Calvin and Zwingli, as well as innumerable others, who disagreed with Luther. This is spiritual entropy. It is also precisely the problem with all of protestantism. What ECT has done is to re-emphasize and re-establish knowledge of our common beliefs, which is very useful for both ecumenism as well as serving the cause of Christian unity.
From the viewpoint of someone who has come into the Catholic Church, the main task toward Christian unity is for non-Catholics to deny themselves and take up their crosses in open-hearted study of the truth of the Catholic faith. ECT has been a great help in this regard, but we are not true to the Lord if we do not lead you, in all charity, toward the fulness of faith as found in the One, Holy Catholic and Apostolic Church.
Simply as a practical matter, the Catholic Church is the last and best hope for Christian unity in the world, regardless of whether or not you currently agree with her teaching. We can argue the reasons until the Lord calls, but facts is facts, so to speak.
Christ’s peace be with you.