I took for it was recommended to be safe for breastfeeding.
It seems because it does not have estrogen, it tends to have milder side effects than combined pills. Anyway, I didn't experience any bad side effects or rather noticed anything that bothered me. My periods were irregular as expected with breastfeeding. Also i don't think it affected my milk supply in any way.
The reliability of the progesteron only pill may be slightly less than that of the combined pill. But i remember being told that the first month of use is a little unsafe so you might want to be a little
careful and use additional precaution to avoid pregnancy. Also don't forget to take
the pill at precisely the same time everyday to be effective. There can absolutely be no missed pills.
Hope that helps and happy breastfeeding.