I bought this in two sizes (12 mo and 18 mo) for the summer.  Right now, the 12 mo. fits my 11 mo. old best, but they will both work in a pinch.  I've bough several different brands of swim diapers to try out and like this one the best.  It's got side snaps which make getting it on/off a lot easier (or getting a disposable diaper or prefold worn underneath while you're transporting baby to the pool easier to get off).  I like that the iPlay has a little bit of absorbent material in the diaper.  Unlike the other swim diaper covers we have, it will absorb a little bit of pee if baby goes while you're holding him before you get into the water (which we experienced the other day right before swim lessons!  This kept my husband dry unlike the week before when my daughter peed through her diaper cover onto my lap).  I haven't had any experiences yet with how well it "contains" a real "accident", but the legs seem tight enough to hold everything in.

Edit: 4/25/2013 - after using this for several weeks, I have to downgrade to 4 stars.  While still a good diaper, the snaps on the side aren't sturdy and some don't even actually clasp, meaning I must make sure there's an additional layer (I've been using a different brand swim diaper) on top of this swim diaper or it could unsnap and fall off.  Kind of disappointing since it's such a good product if it would just stay together!