I've got a M24-5 with Soaps in JJ positions:
I've had it about 6 weeks. My impressions are that it has great tonal variety. I also have a stock (i.e. all Fender) franken-Jazz with singles. My sense is that if the snappy bright single-coil sound is your ideal, then soap-bars in JJ positions might not be your exact cup of tea. Since I already had the single-coil sound in my tonal palette, I was shooting for something different but not completely estranged from the best Fender-esque bass sounds.
I also have an 1977 Alembic Series I. This might be a strange way to put it, but if my Jazz and my Alembic had a baby, it would come out something like this Sadowsky. There's great transparency of tone, and great variation in timbre depending on where & how I attack the strings. (which is a characteristic somewhat more of the Alembic than the Jazz). But the overall timbre doesn't scream ACTIVE BASS.
What's really nice is that just the passive circuit quite sonically interesting. Then you add in the option of the Treble & Bass boost and you've really got useful variety.
I've mostly been running passive and using pickup panning for tonal variation. I also dial in about 10% bass and about 5% treble and back off the VTC about 10% - this is a great sound.
I still feel like there's much to learn about what the tone circuitry of this bass can do.
One qualification: I had a question about this bass and Roger determined that the bridge pickup wasn't performing quite to specifications. Roger quickly shipped me a replacement which has only been in the bass for 2 days and which I have yet to gig with. So I've really only had a short time to form impressions with the pickups running at full proper specs.
Finally, the official word from the man himself, when I asked about soapbars in JJ positions: "It sounds like a J but bigger and fatter."
I generally agree with that statement, although in my case the woods were chosen not to be your classic Maple/Ash or Rosewood/Alder combination. To my ears, with this wood combination (Ebony board/Mahogony body/Walnut top), I hear more similarities to a PJ configuration than the classic JJ snap.
Final two qualifications:
- I'm definitely more of a meat and potatoes player - I don't slap much. So I haven't thoroughly explored that sonic territory
- Your mileage may vary

I hard to write lucidly about sound. I will try to post some recordings.