Sounds like Flatwound. ALL bass strings were flatwound originally. The roundwound strings that we're all so used to, didn't really get widely used until the 70's.
Flats will tend to give you a warmer thuddier sound, with less high end, less string noise, and less definition. Listen to some Motown (Flats on a P) or some Bob Marley (Flats on a J) or old Sly and the family Stone (slapping on flats) for classic flatwound sound.
Whether you like the feel or the sound is completely taste and depends quite a bit on what you are using em for.
The trade off is that you can't really add that modern, round wound sizzle to a set of flats. Live, i find I can approximate the flat sound fairly well on a set of roundwounds by rolling the passive treble control all the way off on my bass, especially with deader strings. Recording, I don't think there's any substitute for real flats.