Bluetooth speakers are generally a compromise. You're giving up the high-fidelity in exchange for volume. With the treVolo S, BenQ gives you everything you could possibly want: portability, fidelity, and quality.
To keep the overall package as small as possible, BenQ adopted electrostatic loudspeakers (ESL), where the sound is generated on a membrane that's actually suspended in an electrostatic field (how it works). This allows for a ridiculously loud sound at a fraction of space without sacrificing any quality. And because the sound travels both towards you and behind the speaker, you can take advantage of the natural acoustics of a corner to increase the sound even more.
The treVolo S offer two modes: natural sound, which plays the song as it is intended, and spacious sound, a one-touch equaliser that pushes the limits of sound richness without any distortion. Needless to say I've left it in this mode, savouring my music everywhere in the house, not just in front of the stereo. Unfortunately words can't give this speaker justice: the highs are crisp and the bass is strong without being overwhelming.
Albeit weighting nearly a kilogram, the treVolo S is truly portable with an 18-hour battery life and the handy carrier bag that comes in the box. When you hold it, it does not feel cheap. Set up is easy: find a suitable spot for the speaker — a flat surface works best — turn it on, open up the speakers, then press and hold the Bluetooth button until the blue LED comes on. Pair up and start playing. In a pinch you can also connect the treVolo S to a laptop as a USB speaker. It also comes with a 3.5 mm input at the back if you're a bit retro like me.
BenQ's treVolo S sells on Amazon for $199 USD. It packs two 12W woofers, dual amplifiers, and dual passive radiators. You can even buy two of them and pair them for either party or stereo mode.