I put the BL-05S and Focal Utopia through a real-test tonight.
tl:dr - I previously mentioned the 05S was a bit flat in comparison, and that is still true and I expand on that. The 05S trades accuracy for a touch more vivid, engaging sound, yet is still alive/real feeling. Incredible value (even after customizing your ride with a deluxe 16-core uber-Litz cable upgrade and new tips). I have a new affection for Jade Green.
In addition to an assortment of instrumental hiphop, electronic (Lycoriscoris), psychedelic rock (Circulatory System), ambient, the main piece of comparison was
Khatia Buniatishvili Sergei Rachmaninoff piano concertos Nos 2 & 3 with Paavo Järvi / recorded with the Czech Philharmonic Orchestra, at Rudolfinum, Dvorak Hall, Prague.
This is a fantastic recording and true test for any headphone. Piano is among the most challenging instruments to record - and reproduce - in audio. Khatia's performance is intense in its precision and expression. The dimensional acoustics of the Dvorak Hall is everpresent.
The BL-05S is definitely the real deal. On the merits of frequency response and tuning the BL-05S is truly among the top in terms of presentation. The tuning on it's own is an achievement.
The BL-05S is uniformly strong in its flexibility across many genres. I would say covering even more ground than the Utopia in part due to the Focals bass roll off. The 05S can be more enjoyable on pieces where bass is formative.
The primary difference is that the Utopia, is both drier, yet more faithful to the recording and timbre of the instruments, and brings with it a larger dynamic range, transparency, headroom, and dimensionality. The physical characteristic of each also factor in (i.e. larger driver and enclosure on the Utopia., etc). The 05S is still very vivid, and its presence combined with its low end is engaging overall. The Utopia is also less fatiguing - the sound is completely transparent, even when you turn the Utopia up to get more of an impact. Add a bit of EQ to the Utopia's low end or add a SubPac and it is essentially perfect.
However, there are aspects to the 05S, that are entirely unique. In part, it is the IEM world, the slightly boxed in yet cavernous feeling, the real reverberation from its more sealed enclosure. You can easily sink into anything with this IEM. The right tips and fit are so so important with any iem, and true in this case. I'm going to invest in better because like
@gshb mentioned for another BLON
If I could tell myself what headphone to start with in the audio journey it wouldn't be the HD650 - it would be the Blon BL-05S. I have a feeling, as others have also stated, that there is something about the 05S that will keep bringing them back, even over their other headphones.
For your Driams.