Looking through the GitHub and the AudioScienceReview link - this appears to be specifically about firmware features. You'd need to ensure that hardware inputs on device have input impedance of at least 250Kohms, probably closer to 1Megohm to prevent loading and signal loss if plugging guitar right in. I'd also assume (didn't see confirmation) that I/O is at line level, which is significantly higher than instrument (passive guitar) level, but this device can clearly add/adjust gain along the way. If you use active pickups with a built-in preamp like EMGs, it would probably work just fine.

No, like I commented earlier it's a (digital) audio output from USB only and the DSP part is mostly filters that wouldn't be musically very useful.

But there seems to be new features being planned all the time, so who knows what it might do in the future.