MIM Jazzes come with Fender Flats. Remember, roundwounds will slowly but surely damage your fretboard. People play flats for years with little or no signs of wear, but expect a trip to the repair shop yearly if you use rounds.
Using rounds will chew up a fretless board really quickly and is not a good idea unless you are sponsored ...or otherwise independantly wealthy!
2 basses
I just posted the same link in the DIY thread, but seeing as you asked ... it's the one on the right.
Mity Mite Alder body nitro black finish, front rout, Duncan SJB1's , BA II bridge (not in this photo), MIM Fender lined fretless with stock keys and a graphtech nut. DIY assembly, Pro setup after I finished. D'Addario Chromes (my fav string on a fretless, yes even more than TIJF's which I like on fretted basses. Chromes are 'woodier' to my ear).
About $400 into this one. and it smokes most every other fretless J I've played. The MIM neck is sweet. This is a phenomenally easy bass to play. As far as genre goes. It's open season. I wouldn't do hard rock covers with it but blues, my impression of jazz, r&B, songwriter duo stuff, dub. It works for all those easily.
Fretless takes a little while to get going if you're a fretted player. I find the lines to be helpful when I'm practicing. A purist will tell you it's a bad idea and that your intonation should be exclusively by ear. I like the training wheels though! I play fewer notes fretless. Those notes are very percusive. A different and slower attack than fretted and generally less sustain. Kinda of approaching the upright vibe. I tend towards quarter note lines with a swing feel just by picking it up.
Is it a necesssity, if you're a studio guy it sure is. If you're just a working stiff probably not. It will expand your voice and very likely your musicality though and for hat reason alone a 4 string fretless is a worthy addition to your quiver.