These really are a superior set of strings for the right player. I think they have a lot of character that belies the fact they're flatwound. I think there is a strong low and hi mid presence in them, there is no dull thump. On a jazz, they definitely have that growl.
Also, there's no doubt that you'll get years of use out of them if you treat them well. My last set lasted about six years of moderate use and I just put on another set.
I think the biggest potential drawback with this set of strings is the feel. They are loose, and by loose I mean bend right off the fingerboard loose when you're not used to them. Even after playing them for a decade, I'm not sure I like that aspect of them or not, and there is a bit of an adjustment in playing style when I go from bass to bass (only one of my basses has the Jazz Flats on them). I have them on my Roscoe Beck, and they really sound fantastic on that.
My recommendation to fellow bass players is that if they have any interest at all in flatwounds, they should give this set a try one time. Keep them on long enough to get past the "Oh my gosh, I'm bending these off the neck" stage. After about a week, I would imagine you'll know if these are for you or not.
Quick note as to cost: yep, they're really expensive. However, I might have gone through 20-50 sets of strings in the amount of time these give high quality sound, so they have great value, if you find they fit your style of playing.
Pros - The sound, the balance and the feel. Last 4 ever.
Cons - Price
I bought two sets used. I paid avg. $40/set. They were broken in, but not abused. One set went on a Lakland 4401 and the other Ibanez SR530 both with Bartolini MK1 pick ups. I did not find these floppy at all, I did have to adjust my truss rod no big deal. These are the most balanced strings I've ever played, the tone is just perfect across the board. The feel is smooth , not as smooth as DR Legends. They are flexible which I like. I have tried DR, Fender,Chromes, GHS Pflats, and Ernie Ball. All great strings in their own right. The TI's just sit above them. Look for a set used, they are worth the wait and price.
over the last couple years I have tried a few different flats ... Chromes , LaBellas Reg & low tension , Sadowsky , Fender ... but I keep coming back to the Ti JF344 set ... yes they are very low tension , yes they feel rather floppy , yes I usually have to adjust my truss/action , yes they sound like crap when you first put them on ... but , when they are broke in , they stay just like that for a long time .. ! I realize they have a love it or hate it kinda feel and tone ..
but for the bass that wears Flats in my house ... Ti is it .. ! expensive or not . ... if you can find a good used set , that's really the best way to go ... !!!