My understanding with the Savinelli Roma pipes is that they are rubber stemmed. For about $10-$15 more, they sell the Roma Lucite model, which is the same nice looking Roma with acrylic stems.
One nice feature of the acrylic stem Romas is you can get some attractive, and unique, color patterns on them.
I don't think modern vulcanite stems are as good as those from decades past. My '59 London Comoy's vulcanite is a cut above any other in my rotation. And I usually have to invest at least 30 minutes on a new Grabow to clean up theirs to my liking.
So unless it is a mouth feel issue, I normally steer those on the fence to the acrylic ones. It's worth the extra couple dollars in most instances with a new factory pipe.