I own 3 Sandberg California Superlights and I enjoy playing each of them. No regrets, though I encountered some...quirks.
TM4: 5lb-8oz, Active/Passive, Humbucker/Single toggle at bridge, round-wound strings
TM5: 6lb-8oz, Active/Passive, Humbucker/Single toggle at bridge, flat-wound strings
VS4: 5lb-9oz, Passive, P-bass config, flat-wound strings
As mentioned previously, the body wood is paulownia. It is extremely light weight and very low density. Of course, the weight savings is pretty significant - like unbelievably light. Everyone who has held my SLs are simply amazed at how light they feel in the hands. However, the low density bodies/finishes are more vulnerable to scratches, dings and abrasions than more traditional bodies/finishes. You can scratch it with your fingernail (if I had any - I play bass, duh). That said, this really seems to be more of a cosmetic issue rather than a structural issue as otherwise the bodies have been extremely stable. Balance is great - no issues with neck-dive on mine.
The high-stress mounting points on the body are reinforced using wood inserts. For example, the bridge area has round inserts that are made of much harder wood (one for each bridge screw, IIRC).
Speaking of the bridge, I'm really not a fan of the Sandberg bridge. Don't get me wrong: they are fully functional and secure once adjusted. But I find them very "fiddly" to adjust. Adjustments have been stable once locked in, but if I want to swap strings, it's a bit of a PITA. At some point I might look into replacement bridges, but it comes up so infrequently, that I'll probably leave it.
I found the neck pocket on the TM4 and TM5 were just a bit too deep. Meaning that the G string action was a tad too high for me even when the G string saddle had bottomed out on the bridge plate (I'm a mostly light-touch player). The solution was simple: I installed 3mm full-pocket neck shims on both the TM4 and TM5 in order to achieve lower action on the G string. VS4 neck pocket was fine. YMMV.
I have found the PUPs to be good. Meaning that they are a good match with my equipment and the styles of music that I play such that I am not looking to change them. I'm ambivalent about the pre-amp on the TM4/TM5...usually get most of my tone shaping from the SansAmp and occasionally use the bass tone controls to tweak for a song-specific need.
The necks have been just stellar. Stable tuners, smooth fret ends, plek'd/polished/level frets, well finished woods, good alignment with the bodies and simple to adjust truss rod for different string tensions. Thanks to my Sandbergs, I'm now a big fan of the zero fret/string guide design approach.