These booties do exactly what they claim to do...stay on.  I actually just purchased 2 more pairs because I prefer them more than socks, that fall off my baby's feet.  They fit true to size for my son, who's 7 months old.

The only con is that I wish the fleece was more like a butter fleece.  After one washing they don't look as soft, but the fact that they stay on overrides that issue.

They are worth the investment.