Although neither Asymmetrico nor Mattone immediately strike me as minimalist, I guess given some of the massive, complicated, and visually awkward seat bags out there, I’ll concede that they are. Certainly the Mattone; Asym is pushing it a little more with all the “technical features,” though.
Anyway, I use a Mattone, and like it pretty much, although there are a few things Silca should tidy up with a v2.0 Mattone, e.g. better water resistance, the zipper fflap moved to the upper to make access easier, and the removal of that silly, internal divider. I’d also like to see a slimmer variant; there’s plenty of space in there gravel essentials, and more than enough for road…assuming the desire for a minimalist bag coincides with a minimalist road repair kit.
I use Mattone for gravel, and like the Boa because it’s easier to keep clean than hook and loop. I also like that it’s lined, which give a refined feel, as does the Boa strap, although the Boa loses a lot of potential functionality because the pack is essentially upside down, with the flap on the bottom, meaning you can’t loosen the strap to dig around in the bag because everything would just fall out. With the zip on top, it would allow quick access. Again, an easy v2.0 upgrade.
I also use the Lezyne Micro Caddy, which is definitely minimalist and just fine, but mostly I’ve used Cyckit Aeroclam on my main roadies over the past 10 years. Minimalist in terms of packing capacity (for the standard model), I’m not sure if a seat-hugging, molded hardcase can be considered minimalist, but it fits high n’ tight to the saddle, and I like them.
Cyckit Aeroclam