Here's what I suspect may be what's going on:
MTD, who LaBella manufactures strings for, had a special NAMM batch done, in which they polished the strings for a smoother,"buttery" feel, then offered as a special exclusive set. Here they are at Michael's web store:
MTD Super Polished Bass Strings — Michael Tobias Design
Seems like this was a test run, and evidently enough success that they've developed a permanent place in the LaBella line up. Funny how the "butter" moniker stuck. Not sure if they're exactly the same formulation strings that they produce for MTD, as they are not mentioning a tapered "B", but it seems most likely that's where the
concept started.
Would be nice to hear from any MTD Super Polished users regarding how they feel. I've been considering a set for my fretless, as I am strictly a round wound user, but a string that's just a
little nicer to the fretboard seems like a good idea.
As for the price, well, yeah, it's an additional process, so it's going to cost a bit more.