I received this guitar with a terrible problem/defect that I can't possibly fix by myself, and I think it should be sent back to the Ibanez factory for an inspection, so I'm returning it.
The third fret from the nut is way higher than the others, it's not level, and when I press the the B note on the 5th string (but also all the other notes and strings at the second fret) I hear a terrible buzz, caused by that third fret being too high and stuck in the way, and meddling with the vibration of the string, ruining the clean sound. (The same is not happening with any of the other frets, as when I press the notes on the first one I hear nothing of the kind.)
I tried adjusting the truss rod, but it won't fix the problem unless you lose the tension of the neck so much, to the point where it gets too concave, and it starts creating other intonation and fretting problems. The main issue here isn't the truss rod, but that 3rd fret which has most likely not been inserted or hammered into the wood properly. I won't mess with hammers to fix this, as I can easily damage the guitar; I won't mess with sand paper either, so it is a big: "There's NO WAY I can fix this".
This way this guitar is unusable to me, and I've decided to send it back, asking for a substitution or a refund if it's the case. What a shame, as I liked the design of its thin neck, and I think it's fun to play. I will wait what Thomman says and does, and I will update this review soon with more news, hoping I'll get a better S521 and that not all of them have this awful problem.
------- update, 27 - March - 2023:
I sent it back, and Thomman sent me a new one: this one is pristine, it has no protruding frets, it looks fine, seems new - with no signs of usage, unlike the previous one which had somehow a few tiny signs.
So, I'm quite happy now. I have to advice you that this guitar has no finish, its wood is kind of soft, so if you strum with passion you may dent or create scratches on it with your plectrum, so be careful.
You may need to adjust the truss rod a bit, to make the action the way you want it, and the intonation. I use it for live shows because of its weight: very light. It is nice to have a longer fret-board with up to 24 frets. I've no complaints.