Definitely not a universal device.
Pair it only with the harshest, most bass-deficient IEMs.

Design is good, low noise is good, physical gain switch is good.

But I still can't listen to it for more than 15 minutes.
It's just the awful pillowy bass texture and treble that sounds like nothing.

I see that people really love this dongle, I understand why, I've never heard a DAC that smoothes out the sound so much without losing treble extension or doing something weird.
But it's just not music anymore, it's just sounds.

IEMs used:
Sony XBA 300;
Sony XBA Z5 modded;
Etymotic ER4S copy (same driver with 100ohm resistor in different resin housing);
Simgot EA500;
Tanchjim OLA Bass;
7Hz Timeless.

I've seen people talking about them having insufficient treble, but I can't confirm that, treble rolls off only after 15kHz, which is a nice result.
$30 is an adequate price for Cadenza, nothing groundbreaking.
If you've heard one decent $30 set, you've heard them all, I guess.

Burn in, tip rolling, source rolling (iBasso DC03 Pro, e1da 9038d, xDuoo Link2 BAL) didn't help with eliminating sibilance.

Two cotton heads from cotton swabs, each cut in two, with thicker part being placed inside the nozzle worked.
That trick always works with peaks and overall bad treble.
Frequency response smoothes out, bringing recessed parts up and all the peaky parts down.
Which means less lower treble and more upper treble.
Also tilts the sound towards bass. Requires much more power afterwards, because we've pretty much dampened half of the FR.

I think that CCA CRA is a much better choice in all aspects.
If you like mids, Hola is not that great with them, to be honest, keep searching.

Can't say I feel like I've wasted my money.
Cotton trick worked perfectly, they go from 5/10 to 7.5-8/10 afterwards.
I've seen a lot worse cables alone costing up to $15.
But you'll need to open them up, tear out the filter, cut the cotton correctly and adjust it several times (or dozens, if you're not experienced), while trying to remove channel imbalance that comes from density and volume differences of the cottons inside the nozzles.

I am strongly advising against buying them if you do not intend to mod them.
They do not sound that great and there are lots of $20-$50 IEMs that sound much better.
If you want unique Sony sound, buy EX1000 or EX800ST.

I have fixed them by opening them up and covering the dynamic driver's port with tape and stuffing both nozzles with 2 high-density tuning foams 4x4mm each, you can make you own, or just buy them on some Chinese marketplace.
You need to heat them up before doing that, there's glue holding them together, start with the notch near the MMCX port, press really hard at 45 degree angle and pry the cover out.
Yes, you will scratch them while doing that.
You can see tuning foam used for covering the port of the DD, there isn't nearly enough.
If you want the bass to still be dominant, use a bigger piece of foam instead of taping them up completely.
Afterwards they have 9/10 treble extension/quality/realism, literally the best out of my whole collection (including 7HZ Timeless and HZ Heart Mirror).
I can imagine something that sounds better, but I've never heard it.
Bass sounds good, with good balance and nice sub-bass kick.
Mids are cleared up.
There is some sibilance in the treble, somewhere around 9kHz.
However, I am really treble sensitive and can tolerate it without a problem, it doesn't ruin the sound, you can add more foam into the nozzles and the sibilance will be gone, but you will lose some treble extension/realism, just use warm sources.
The mod is easily reversible, just don't lose these small foams that are already inside.
My score after the mod is 4.5 out of 5.
Sources used: E1DA 9038D with 75ohm adapter, xDuoo Link2 BAL, iBasso DC03 Pro.

For $100 you can buy much more universal iBasso DC03 Pro and a good $20-$30 IEM.
Though I have to say, 9038D has the best upper treble.

Would've been 4.0/5.0 if they didn't fail with imaging that bad.

Sometimes I try to listen to them again.
I get severely disappointed in several seconds and put them far away until the next time.

Treble is mediocre, bass is awful (boomy and textureless).
Mids are good.
You can overcharge it and kill the battery, I mean, how could they actually NOT put a charging controller in there, it's not a 10$ product.
Packaging is kinda good, though no OTA cable, which is a bit hilarious.
In comparison, Cayin N3 obliterates this item in DAC mode.

Stock cable is really, really bad, I thought that cable-believers are silly people before I've purchased MMCX adapters and good copper cable for these earphones.
Considered selling them as many times as realizing that I've nearly made a big mistake.
Bought them for 200$ with shipping.
Was definitely disappointed after first listen. Well, they are seriously source-dependent.

I did like them in 2019.
Today it's just D-tier.

Tested them on Massive Attack tracks (why? because they have insane mixing quality with a lot of kinda quiet, background samples), on some black metal, on noise and power electronics albums - they don't fail in any of this genres.
If you want to get really cinematic experience - tame the highs and lows thorugh an EQ, lift mids a bit. Wait for your brains to adapt.

I remember stopping believing reviewers after getting them.
Multiple graphs show that my unit wasn't faulty.
Complete tuning failure.

It's early KZ, not really good in any way.
Sibilant as hell.
Sounds off.

New version is basically an upgraded version of the old ZS6s.
Less treble fatigue, better balance overall.
Not worth $50 in today's market.

It's kinda interesting that they came with earbud foams included.
They definitely sound better with those on.
But why were they made into an IEM?