If assembled properly, they do not spill at all. We're using them as water bottles that the toddler can use on his own to build independence, and so that part is great. They're really hard to drink out of though. My partner complains that he has to work too hard for the liquid when he tries to steal our kid's water, but maybe kids that are used to baby bottles don't mind so much.
It disassembles and can go in the dishwasher, which is great. But at least in our dishwasher, the ridges in the bottle catch water so we have to give it an extra rinse after the cycle to make sure there's no residue.
I have tried so many sippy cups and straw bottles trying to get my daughter off her milk bottle. This has been the first to work!!! Amazing! Only wish the bottle had a cover, but at this point I don't really care about something so minor. Best transition bottle ever! - from one Happy Mama