Actually, the one I bought screws in place of the nipple. The point is that the percussion caps cause corrosion of the firing pin hole (at least on mine) causing things to freeze up. The 209 doesn't do that since the "fire" is contained. Unless you live in a open ignition state (I do) changing to primers isn't a big deal. In an open ignition state, you can bore a hole to let the rain get in and foul your cap. Oh well...
yes, its the one that replaces the #11 nipple. I load for shotgun, so I've got several hundred primers laying around. figured it'd be a better option, that and I don't want a FTF. Want the hottest spark I can get in there.