Kleen Kanteen Sippy Cup

I'm about to buy my son the Kleen Kanteen cups, but some commentators say that the online leaks when the child takes a sip! and others love it. I know Kleen Kanteen products are good, but the beak is Advent.
My son is currently Cup Nuby BPA free spout and I hate it, it leaks down and my son when he gets on the ground, it just pours. Then he drinks milk with Gerber regular cups that I like, unfortunately, they are not BPA free.
So what do you think? Does it leak or not?
because I remember when he was a baby he used the avent bottles and they have no escape until we went to Babies R Us and they said what they said is not to tighten Cap Coz so too, he lost the seal, and since then we have never had a problem with a leak Advent.
so is there a hint of some people do not know about AVENT sipper?
ps: For those who will tell me the BPA is not dangerous and that we all grew up with BPA please leave your comments to yourself.
Thank you for reading!

I have not had problems with a Kleen Kanteen. My son is two and he is thrown around a lot.

I do not know about the Kleen Kanteen, but I foogoo Sippy cup from Walmart and my son loves and I love it. no leakage can take a beating from falls or being thorwn across the room as the Downer is that what is in one size.