This synth has that early 2000s virtual analog sound like the MC909 or the Access Virus and has the presets to match.
The build is ok but could be better, honestly: the knobs are great and super smooth, the face plate is metal, but the actual synth chassis is plastic and the keyboard is okayish but lacks aftertouch.
Nothing wrong, but nothing premium either.
It's quite light for its size, which is good, and the included bag is of good quality and fits the synth perfectly (kudos to Korg for the included bag!).
The synth excels in evolving sounds and whole rhythmic patterns, thanks to its internal polyrhythmic multitrack sequencer per patch, something others synths don't have and it really shows.
It has a lot of very versatile sounds and evolving synths, but what it seems to excel in is in trance and synthy soundtrack music.
It can be used to emulate 80s synths and has some cool sounding Juno pads and DX7-like bell sounds, so you can easily make an 80s-like soundtrack with this synth alone.
It doesn't really sound the same as a true analog synth though.
I don't know what it is, but the actual quality of the sound lacks something. As if it was sampled at a lower rate or something (which is not the case because that's not how virtual analog synths work, but still).
Maybe it's because of the internal effects: they are very cool but sound a little "grainy" to my ear.
The synth still sounds great though and if I had to keep a single synth, maybe this would be the one just because of how versatile it is.
And the perceived difference with a true analog sound just gives it some character.
The hands-on control is quite convoluted: it has a lot of quirks, but I've seen much worse.
Making your own sounds can be VERY involved, so be warned.
The hardware controls seem to be there to modify the presets, not to make a patch from scratch. I mean, it can be done, but you're much better off using the PC/Mac editor for that, because there's LOTS of menu diving otherwise.
Compared to the Roland Jupiter X/Xm, I like this one better:
The presets are much more inspiring to me and it's actually easier to use, so if I had to choose, even though I'm a fan of Juno sounds and the Jupiter X/Xm has a slightly better sound quality, I would still choose the Korg Multi/Poly, because the Jupiter wants to be so many synths at once that it loses its character in the process. (and the i-arpeggio ends up being kinda gimmicky in the end.)
This synth has that late 90's early 2000's trance energy with some added "Stranger Things" vibe, with Juno pads and DX7 bells.
It's clearly a winner!
Now, this synth also exists in software form.
Is it really worth it getting it in hardware?
If you want hands-on controls for live sound manipulation of presets, then yes, it is worth it: it has plenty of knobs to make the sound evolve live and the kaos pad is very cool to use.
If what you want is to craft your own presets from zero with a knob per function, then no: making your own presets is so involved that you will need the software editor anyways, since the screen on the synth is too minimal for in-depth editing. It can be done, but it's not fun at all.
The software version has the advantage of being able to use as many instances as you like and saving all your edits per track and per project without all the hassle of having to record external hardware.
So its much more convenient if you only want to compose music and not perform it live.
But keep in mind that software licenses are just that: a TEMPORAL license of use that could be revoked at any time for any reason (and that will stop working eventually because of software obsolescence and operating system upgrades).
Hardware on the other hand, you actually OWN IT.