You can't compare it to Volumio. Volumio runs quite a bit of software written by various third parties that don't know about each other. This thing is Roon only, all throughout.
1) The performance is incredible. Boot in <2 seconds, full update (post-download) in ~30s. Everything is snappy and built from the ground up for Roon.
2) It doesn't feel like Linux, or any other operating system. It feels like Roon. There is no point in hooking up a keyboard or display -- you can't do anything. The web UI is small and clean, and does a few tasks very well, and with a lot of information. It is really hard to mess up, and if you do, it's easy to recover. This is a DIY embedded appliance system, not an user controllable operating system.
3) The entire OS is VERY small -- this is including a giant ffmpeg binary for MP3/AAC codecs:
Filesystem Size Used Available Use% Mounted on
/dev/root 1.9G 93.4M 1.7G 5% /
/dev/sda3 1.9G 82.7M 1.8G 4% /roon/app
/dev/sda4 55.0G 182.3M 54.8G 0% /roon/data
4) kernel and modules optimized for audio, and everything is configured to work best with Roon. There is nothing else in the system, so all middle men and hooks are removed. Roon -> kernel -> hardware. That's it.