I got to play it for a bit this afternoon. Short answer, it sounds amazing. I highly recommend it.
Longer answer: It is fat, muscular, maybe a bit wooly, as one expects from a P90ish pup but still brings a very nice clarity to the party. It is articulate and beefy at the same time. I compared it to my EBMM Short Scale Stingray and was surprised that the EBMM has a bit more signal than the Serek. Of course, the EBMM is also a bit brighter and the low end is not as big. The Serek is wired in series rather than with a switch so I compared it with the EBMM in series. It responds really nicely to the tone control with an entire spectrum of very useable sounds.
It is more like the first B90 video from Xavier Zoli (see below) than the later ones with the two pickups. His is the straight ahead single coil rather than the humbucking pup which also brings a little difference. I think the highs are a bit rounder and more subdued on the LZN vs. the single coil version… not a huge difference but I hear it.
It is interesting how that placement impacts the tone. To my ears, you can still tell it is a Mustang. There is something about the placement plus the short scale that imparts something beyond just the pup.
All in all, I am extremely pleased with the results. This bass is a keeper for sure now. Next week I have a rehearsal and a gig so I'll give it a real workout.