I’m a convert from protestantism. I knew almost nothing about my original faith, but I was challenged by reading Karl Keating’s Catholicism and Fundamentalism. (FWIW, Mr. Keating is our host on this Forum).
I began a quest (which would consume several years and thousands of dollars in books, in a pre-internet age). I started with the “protestant fathers” (why not begin on my own turf?)
Finding those arguments unsatisfying (and strangely incompatible) I turned to Catholic sources.
After becoming Catholic, I thought that my studies of Luther, Calvin, Zwingli, etc would prove a valuable asset in apologetic discussions with those who were still protestant. I was wrong. No protestants I have ever talked to had any knowledge of the theology upon which their faith was founded (other than very broad concepts, such as “the Bible”). No protestant was interested in discussing these topics. As a protestant, I had been ignorant of protestant history, and I have never found a protestant who was interested in discussing it.
So there is nothing wrong with reading protestant authors, but don’t expect it to help you if you want to talk to protestants about it. They won’t know, and they won’t care. You won’t come off as “ignorant” if you talk to a Presbyterian and you haven’t read Calvin’s Institutes. He hasn’t read it either. He might not have even heard of it, and he won’t be interested in discussing it with you (you will actually intimidate him if you reveal that you know anything about it, because he does not).