I have to say that despite the bad reviews here, the headphones are amazing. I dropped them, stepped on them, threw them around, and I've had them for over half a year and they haven't suffered any damage at all.
However, the battery is unpredictable. But I have noticed that when I leave them to charge for a longer time, even when it says they are fully charged, they last longer. It might have to do with the fact that I mishandle them.
The app is perfect, the sound, the connection, everything is perfect, even during calls. Just be careful when you let the battery completely drain, because after you charge them and reconnect them the next time, the mobile indicator will show that they have 10% battery again. Don't worry, it will fix itself within 2 minutes and work normally afterwards.

After two months of use, they disconnected from both devices after the first ten minutes. I discovered it while driving for the first time. I will exchange them, but they seem completely unreliable.

Update 15/01/2020: It seems that the first set was simply defective. They immediately replaced them at the store where I bought them, and the new set is fine. Both devices (two Xiaomi phones) connect instantly and without any problems. Pairing is also easy. The sound quality during calls is satisfactory, both on the earpiece and the microphone. In media playback, I notice a slight delay between audio and video, but that's not the intended use anyway. I'm changing my rating from 1 star to 4, due to the delay and because I don't have an opinion on durability yet.

Μετά από την φόρτιση το σήμα που δίνει στη συσκευή του κινητού είναι ψευδές. Λέει ότι η μπαταρία είναι στο 10% με αποτέλεσμα να κάνει έναν ενοχλητικό ήχο κατά τη διάρκεια της χρήσης. Η δε μπαταρία του δεν κρατά επουδενί 8 ώρες όπως αναφέρεται στα τεχνικά χαρακτηριστικά. Όλα αυτά από την πρώτη μέρα. Μια αγορά που μετάνιωσα. Τώρα που γνώρισα το προϊόν με όλα αυτά τα προβλήματα δεν θα έδινα ούτε 10€.

Ένα handsfree με διάρκεια μπαταρίας 4ωρων (δεν φτάνει τις πέντε ώρες αν μιλήσεις 15 λεπτά απο πλήρη φόρτιση) δεν έχει λόγο ύπαρξης χρηστικά για κάποιον ακόμα κι αν ο ήχος του είναι ικανοποιητικός .

The worst thing there is. The battery doesn't last more than half a day with 3-4 calls lasting 1 to 2 minutes each. I'm really crying for the money I spent.