@rein: Costume lenses are made to be part of a costume and there's an assumption that people won't be wearing them for too long without taking them out (ie it's not like people will wear them for an 8-hour work shift). Normal contacts are always pushing for things like letting liquid pass through and being safe to wear for extended periods of time while costume lenses focus more on their looks and things that will enhance that. Costume lenses aren't unsafe or anything like that, assuming you're wearing them like they're supposed to be warn, but they usually come with a warning advising against prolonged usage.
@Kurohige: Posts pics of how they look. I started to buy the 3 pronged version a few years ago but I read that these types of lenses are a waste if your eyes are dark because the color won't show up that well. My eyes are dark brown to it was a no go. I'd be interested in seeing how they look on you, especially if you have dark eyes.