yes, safe during breastfeeding, as long as you are asking about anything passing through your milk. Of course, with any birth control method, there are some risks. Many women also use both regular and low dose birth control pills while breastfeeding. Reviews are mixed as to whether or not hormones pass through the milk. Sometimes they are given to women because the the chances of another pregnancy pose a greater high risk situation than the potential for small doses of hormones passing through the milk.
For me personally, I would not take the risk of any hormonal birth control, not even the hormones that are in the Mirena IUD. I too would choose the Para Guard Copper IUD while bfing. In fact, I'm 7 weeks postpartum and have an appointment for an insertion in 2 weeks. We'll see how it goes!