I use a Convatec convex moldable with a full Eakin seal, placing the Eakin snuggly around the stoma and then the wafer on top. I am also diligent with my "heat & pressure" routine to get them set and melded together.
I do believe the idea behind the moldable was that it does not need a barrier ring, but I don't think the moldable alone would work for me even though my stoma sticks out far enough. Maybe it is just a security thing, but the way I see it is, "if it ain't broke, don't fix it"