None of them will sound particularly acoustic. I actually appreciate the NS line more because they're not trying to make a fake acoustic instrument; they're making proper electric ones.
I think your comment is totally on the mark!
I have only played a 6-String US Series NS Design. The Current EU series is supposed to be made to the same spec. I thought the bass was incredible, but it was absolutely nothing like a real acoustic string bass.
Differences
-The NSD had very little attack. Overall the tone was more like fretless electric, but I found it impossible to get punch or thump on the front end of the notes. The notes sort of bloom out of the instrument.
- The instrument also has really long sustain, which makes it sound even less like an acoustic bass. I am talking the sort of sustain that requires a compressor with most instruments.
- Due to the long strings, the NS Design produced an exceptionally strong fundamental that few bass players are likely to experience. I thought the B-string was especially noteworthy....BWAAAAAAAH.
I tried using an EQ boost in the low mids to produce some thump, and also tried using foam and cloth under the strings to dampen some of the sustain. IMHO both degraded the instruments natural voice.
In my experience, mutes tend to only work across a limited range. So if you get the mutes dialed in so the low end is enhanced, the high end of the instrument will sound bad. The was really obvious on the instrument I had since it was a 6-string.
After some experimentation I decided to accept the instrument for what it was. I sometimes used it for jazz combo, but to be honest it felt really weird playing medium swing standards; even more weird than playing the tunes on my fretted Yamaha TRB6P.
The place I used it most was in big band. We played a pretty wide mix of music, ranging from 40s era swing to modern compositions, and even threw in some fusiony Stevie Wonder vocal charts. When space allowed I would set up a real string bass, my TRB6P, and the NS Design. I used the TRB6P for more funky stuff and the NS Design for modern and fusiony stuff. The more traditional pieces were played in a string bass.
On occasion when stage space was extremely limited, I would play the whole show on the NS Design. I didn't think it was ideal, but I got the impression that I am the only one that really cared. We sometimes had receptions after our shows and the everyone I spoke to thought the NS Design sounded fabulous. They were also very curious since it is sort of an unusual looking instrument.
I was a military musian and the NS Design was the only bass I ever asked to be bought specifically for me. All of the bass guitars and string basses I played over the year were exising instruments that I checked out of supply. And of course when I retired I had to turn in all of my military gear. The piece I miss most is the NS Design bass. But IMHO it's not a very good substitue for a real string bass. I would say it had a voice that was unlike any other instrument I have ever played.
Here's a video I found with an EU5.