Since I just bought it today, all I can tell you is that Zo drank her water, with it in there, without any objection. A good start, at least.
The thing is, she's young (15 months) and her teeth are great. I just want to keep them that way. My poor little Phoebe had only 3 teeth left at 17-1/2 and I sure don't want that to happen to Zoey.