As long as the volume setting is below 50%, the sound produced is relatively weak. It is sufficient only for a small, enclosed space, without other sources of noise. However, after half of the volume, things change significantly: the speaker becomes much more responsive and the sound strengthens with greater progress. In an open space (park), with the volume at around 80%, people could pleasantly and clearly hear the music within a radius of 5-7 meters. Of course, it is not suitable for parties, but that is not the goal of the speaker. In summary, the sensitivity of the speaker is not linear, after half of the volume it starts to "come alive". Personally, I find this positive because it ensures (to some extent) that the speaker does not reach full volume and the sound does not become distorted.
In terms of frequency response, it is quite lively, but with "sweet" highs that are not bothersome. Clear sound, in most genres of music, with an apparent (and pleasant) neutrality, a characteristic of Sony. Do not expect the "wild" midrange and highs of speakers from other brands, which are targeted for party situations.
Regarding bass, it is decent at all volumes and with most genres of music (dance, pop, metal). In extremely low bass (for example, trap productions), the speaker cannot reproduce sound from certain Hz and below, but we are always talking about frequencies that are intended for reproduction by subwoofers...
The user interface (operation, connectivity) is the best I have encountered so far: simple, minimalistic, fast. Very well-designed to make its use easy. It has large buttons, few and multifunctional, small LED indicators, overall very user-friendly.
The strap is of good quality and useful, the speaker in general is lightweight and appears sturdy. I have not tested its water resistance.
Finally, the charging port is not the same as the universal one that many devices have (Android phones, tablets, etc.), so a little extra attention is needed not to lose the charging cable.
In conclusion, for its category, the very small Bluetooth speakers, it is a very good purchase: exceptional sound, non-linear but ultimately high volume, more than sufficient, fantastic, simple user interface, good build quality (with a metal speaker grille). In its category, there are cheaper options, but time will tell if it ultimately wins its value with its overall quality. For now, I find it to be the best value for money.