I stumbled accross this interview of BY's descendent who came out of Mormonism. It's actually a remarkable testimony. Praise be to the Lord!
It's worth listening to, even if you have time only for the first few minutes (link).
It actually exposes the same flaw that we see in other false gospels:
1. Undermine the value or the reliability of Scripture.
2. Identify your church's teaching as a necessary supplement.
3. Complain against those who wish to return to the Bible alone.