I got mine when DS2 was about 7 months old I think, and didn't find that it had any effect on bfing at all. I did have a few weeks of spotting but it wasn't too bad, and after that settled down I found AF was less frequent and much lighter.

The one thing I can say is that there a lot of potential, minor side-effects. But it is not expensive to get, and is VERY easily removed. So if you are worried, you could always try it and remove it if you're not happy.