Regarding the Activity Tracker:
Positives: The mobile application is easy to use, it connects and syncs quickly. I consider the measurements to be accurate and the battery lasts satisfactorily (about 2 days).
Negatives: The construction quality is mediocre. It doesn't scratch easily, but after 2 months, the screen glass came off and when I tried to put it back, the surface of the pixels broke. Also, it requires a bit of attention not to come unbuttoned while wearing it.

Regarding the headphones:
Positives: The price you get them with the Tracker is very low (around €7-8), as well as their quality. The sound is very good, with enough volume (you don't hear external sounds, e.g. on the street, in public transportation). The bass is strong and the sound doesn't distort. They connect quickly, without interruptions (on Xiaomi Redmi 10. On a laptop, it cuts off occasionally. The Bluetooth version probably plays a role). They are comfortable in the ear, they don't fall off at all.
Negatives: The material of the headphones, especially the case, is very slippery in the hands, and if they fall while in motion, damage is certain. But the worst part is the battery life. The right earphone lasts only 30 minutes from the beginning. The left one started with over an hour of duration, but after 2 months of use, it ended up lasting only half an hour, while the base needs daily charging. The sound quality performance is also declining. I replaced them with the Fineblue ones, which are excellent!