Thanks, that was really helpful.  A couple pages back is a link to a Japanese company, Rosso Corsa, that makes a lure called the Vodka, where the lip can be popped out and turned around.  One side is flat, the other is slightly rounded.  It's an interesting concept, but the lure is $20, and I need some reassurance that the lip won't fall out after 3 fish.

Although the Calappa comes with an optional separate lip it is the same means (snap fit) of attaching it as the Vodka. That said I have never had a problem with the lip failing as it has a very positive fit leaving no play.

I would be a bit less worried about the Calappa, because I would have no reason to ever remove it, like if I were to flip it around on the Vodka.  Still, that's good to know.