I believe it is to do with how the basket is retained in the portafilter (I.e. how tight the spring is).
I have only ever had ridgeless baskets (which seem to be the preferred option around here).
Take your existing basket out and have a look at it. If it has a ridge around the circumference of the wall, then you might need a new retaining spring/clip to use a ridgeless basket. Otherwise you should be good to go.