Thomastik makes a heavier type of rounds, but I don't know much about them. Maybe a blend between sets?
Thomastik make TWO types of heavier roundwounds. Both are completely different from the Jazz Flats/Rounds. Like all Thomastik bass strings they're only available in ONE gauge, take it or leave it.
The Infeld Superalloys 45-105 are the most similar to roundwounds from other manufacturers. Compared to D'Addario XLs (which most bass players have probably tested at some point) the Superalloys have slightly smoother highs and a stronger, but less "clanky" mid range presence. They also last significantly longer than XLs. Very good strings for a "middle of the road" roundwound but they're not totally unique strings like TI's Jazz Flats/Rounds. Much more similar to standard nickle plated roundwound strings.
The Powerbass 47-107 sets are more unique. I suspect they must have a VERY thin core because they are a lot more supple/bouncy than you would expect from the relatively heavy gauges. If I didn't know they were hex core I would have been convinced they were round core. They somehow manage to feel soft/supple and kinda bulky under the fingers at the same time. They start out very bright, with amazing clarity for chords but they also mellow out very fast. I don't think I've ever heard strings COMPLETELY change character so fast. Once they've mellowed out they have a rather warm, thick, organic tone that will provide a solid foundation in a song but with enough mid presence to sit nicely in a dense mix. I'm not sure what to compare them with to be honest. I guess they have a bit more organic warmth than most roundwounds. Maybe a TINY step towards the Jazz Rounds tonally but a completely different feel due to the much heavier gauges. They're quite unique but they're also my least favourite Thomastik strings. I can't really make up my mind about them. I seem to like them on some basses and absolutely hate them on others. And it's not just about the tone but also the "feel". Sometimes I love the "bouncy" feel, but sometimes they feel a bit too bulky under the fingers for my taste (which is typically around 45-105 with roundwounds).
As for the Jazz Flats, they're definitely worth the money IMO but whether you like them or not will depend on personal taste and what kind of music you play. Definitely not suitable for old school "thump". Totally unique strings that can't really be compared with anything else. They're quite floppy, especially the A-string, which isn't for everyone. Personally I don't like them on split coil P-basses as I find the strong mid presence of most split coil P-basses combined with the strong mid presence of the Jazz Flats can get a bit too much. I absolutely LOVE them on many other basses though, like SINGLE coil P-basses or long scale Danelectros. The mid presence and nicely balanced lows of TIFJs can be a very nice match for a boomy single coil P or Dano.
I only like the long scale TIJFs. The short scale sets are unplayable IMO, due to the insanely unbalanced tension between E and A (unless you can find the much better balanced "Höfner" sets with the lighter E-string... they're VERY floppy though!!!).