I noticed when shopping for a replacement 9mm bbl for my Springfield Nowlin ramped .38 super that there were several other types noted. Even though my bbl is marked Nowlin, the dealer I got mine from wanted detailed pics of the existing super bbl, and inside of the frame.

I saw a closeup of the RIA and it has a "bump or hump" on the rear face (the area that mates with the frame) of the underlug and there are other makers / types like Clark, para, and in house unspecified ramped bbls. like Springfield.

What are the difference(s) between them and do any have specific advantages?

the rounded Clark/Para cut is easier to machine on a receiver not originally fitted, just a simple 3/8" (IIRC) cutter works... the Nowlin requires the frame be milled vertically as the cut is square and uses the end of the cutter that is extended for clearance

I always perceived that the Clark cut was stronger with less chance for stress cracks in the frame YMMV