They didnt leak for us, but we only tried them a couple times. My LO is BF and refuses all bottles. The nipple is the same as the MAM pacifiers, so if your LO takes those, s/he will probably take the MAM bottle too. Good luck!
I hated them. They leaked like crazy. I ended up throwing them out after the first week. I prefer the Vente Air bottles from Playtex. It's the same concept, but much way less problems.
Re: MAM bottles