Purchased at €20.96 and I've been using them for a month.

Usage: Discord calls, gaming, series, music

Negatives: 1. Does not include an adapter/splitter (!!!) for use on a computer for audio/microphone—you have to buy it yourself, 2. Poor build quality, I don't know how long they would last if I didn't use them only for the PC, 3. The cable might be short for some people and gets tangled from time to time, 4. Does not perfectly isolate sound inside the headphones when it's loud, 5. The sound may not be loud enough for some people.

Positives: 1. I haven't personally tested it but from calls, my interlocutors have been satisfied and like the sound of the microphone, 2. The microphone is detachable (so theoretically you can take them outside as regular and not just gaming headphones, but I've noticed that without the headphone mic, the interlocutor can't hear me from the phone's mic—all this if you're not worried about their durability due to the poor build quality), 3. Has surround sound, 4. Has a mute button, 5. Has a volume wheel.

In short, they're good headphones if you use them like I do, I don't know what happens if you put them under more strain and if they're likely to break more easily. For €20, considering the surround sound/microphone and their general capabilities, if you're looking for budget headphones that meet your needs, they're a good choice.

UPDATE: broke after 3 years bruh, worth

I really don't know what's stopping me from starting to curse badly. FOR YOUR OWN GOOD, DO NOT BUY them, it's a waste of money!!!!!!
NEGATIVES
1. terrible bass 0 (even though I'm not demanding)
2. awful quality, very poor and cheap construction, something acceptable from jbl
3. horrible sound, my lice have better sound! it's really laughable
4. very bad surround sound, which means NO for gaming.
POSITIVES
1. relatively good sound isolation from the external environment thanks to its design, which goes into the positives.
CONCLUSION, don't buy them unless you want to throw away your money. Also, I should mention that they are not suitable for everyday use if someone wants to listen to their music. Stay away.

For anyone looking for cheap but good headphones, go for the two options I will mention below.
1. sades, any model you want because they are all good. Personally, I have the Mpower, which are better than the razer ones I had for around 20€.
2. zero ground, you may know it, reliability and quality for around 25 euros.

I expected better build quality from the JBL brand. It's not bad for the 35 euros I paid, but two things bother me. The first is that the cable is too short. If you want to connect it to the back of a computer that is on the floor under the desk, the cable doesn't reach. I had to buy an extension.
The second thing is that the mechanical parts are made of very thin plastic that doesn't inspire confidence that they will withstand over time. They require careful handling so they don't bend or break, because then they're just disposable. I saw some no-name headphones for 20 euros in a store, and they had a much sturdier construction.
Also, they have a single four-pin connector. If you want to use them for a computer, you need a 4-pin female to dual 3-pin male adapter for the microphone to work.
On the positive side, the sound is good, it has a detachable microphone, volume control, and a mute button on the headset.

January 22, 2022: 13 months later: This is what I was afraid of. The suspension mechanism of one of the headphones broke. Now that it's broken and I see how it's made, it's clear that it won't last long. Sorry JBL, unfortunately, you're finished... :(