I purchased Kali WS-12 together with Kali IN-8's (definitely check IN-8's Thomann page for my review there), so I'll try cover aspects of subwoofer itself, but also the "matching" operation together with IN-8's
1) PACKAGING & DELIVERY
with weight around 29kg, most common carriers like DHL, PPL, UPS etc.. shouldn't have problems with delivery (weight limit applies to single box, so I received WS-12 and pair of IN-8's as 3 separate boxes delivered together)
unlike IN-8's, there's just one "layer" of Kali-branded brown cardboard, no handles or holes (keep this in mind, might be tricky to carry on your own! - subwoofer itself does have handles on sides though, so no problems carrying it around once unpacked), inside the box, actual subwoofer is seated and further protected by thick sturdy "foam corners" (unlike polystyrene on IN-8's),
package includes printed manual (with some information potentially outdated, I recommend checking Kali website for up-to-date pdf manual), and very short 140cm power cable (as mentioned in my Kali IN-8 review, choice was intentional by engineering team to keep costs low on non-crucial aspects),
WS-12 package box is big enough I could put remaining boxes of both Kali IN-8's inside, another very neat detail by Kali!
2) CROSSOVER & DIPS
despite selectable crossover frequency should be a standard nowadays, not all (especially cheaper) subwoofers do have it, Kali do provide plenty options to dip to, which should accommodate any monitors,
let me quote here Kali support I contacted: "The crossovers on the WS-12 are all 4th order (24db/8ve) crossovers. The LP-8/IN-8 setting is an 80Hz crossover that’s designed for volume matching with the IN-8s, assuming a 2.1 setup in free space."
since I got IN-8's, I put dips to IN-8 setting first, but it turned out to be literally worst setting for my room layout and acoustic conditions, thanks to REW (Room EQ Wizard, free software utility for measurements) I figured out 80Hz wasn't doing good, and also the roughly 10dB gain drop of IN-8 preset was cutting away too much with subwoofer placed behind my desk on the floor,
I ended up with dip settings of crossover at 60Hz, -6dB compensation, and -10dB notch at 25Hz on my RME ADI-2 DAC
3) WHY SUBWOOFER?
majority of people misunderstand the "usefulness" of adding a subwoofer to the monitoring setup,
apart from being able to hear ultra low frequencies at any volume (which most common studio monitors cannot reproduce), subwoofer also takes away "stress" from main monitors, letting them "breathe" more resulting in more transparent true sound reproduction,
having a dedicated additional speaker offers flexibility with monitor placement (but also may cause problems if not placed properly to match them), I highly recommend watching ADAM's Audio recent videos at YouTube explaining the concepts of subwoofer
4) SOUND (subjective)
I just love what WS-12, as a drummer I've been always missing "something" when listening to music or mixing, and now finally I can hear/feel the frequency spectrum - just note I am by no means obsessed by bouncy exaggerated bass like many people like,
it's unbelievable how natural low frequencies sound, regardless of volume or density of the mix, I'm starting to really enjoying listening to all sorts of orchestral/movie composed music and soundtracks, but also drum'n'bass and any other purposedly bass-heavy music, where I'm suddenly not loosing any clarity at higher frequencies due to main monitor woofers not being overwhelmed by very low frequencies,
listening to music at lower volumes brings more joy as well (but I'd say Loudness feature of RME ADI-2 DAC helps evening out the human ear perceived frequency curve a lot too),
honestly I can't imagine not listening with subwoofer anymore, it's hard to describe it to someone who doesn't have (or even avoids) subwoofers, but I feel like my musical and mixing experience is now complete
if you already have a set of decent monitors, and looking more something extra to improve/enhance your experience with sound, then definitely start researching subwoofer options, once you do, you'll probably run across Kali WS-12 as a very interesting choice at reasonable price, outperforming the competition at given price range,
regardless of whatever subwoofer you choose, don't underestimate importance of room acoustics, subwoofer placement, crossover adjustments and I definitely encourage measuring your setup frequency and decay response and spend good amount of time trying different positions in the room