Both Butler and Foxe draw upon the old Latin texts known as the Acta Sanctorum.
I read Latin and I've read Foxe and Butler and parts of the Acta and Butler's translation is far more accurate than Foxe's.
Butler's book is indeed polemical. He is highly selective and biased, but he doesn't make stuff up out of whole cloth to make his case.
And Catholics realize this and don't claim that Butler is telling the whole unvarnished story.