I didn't have any problem with it, I've seen it recommended by others with that standard caveat, which you already understand.
For around $200.00 the set is hard to refuse, and it looks pretty good in the bookcase!
While it is not an all-encompassing set, it is still quite a lot, and at that price it's like buying the Fathers by the pound.
What little I have been able to dig into it, I found no overt bias. The translation is about 100 years old now so the English probably could use a little updating, but it is dignified.
I read a little about Schaff, and while studying the Fathers did not convert him to Orthodoxy or Catholicism, it does seem to have influenced his own thinking about sacramental Christianity. Therefore I think the Patristic literature was more of an influence on him than the other way around.
+T+
Michael