1) Sound. A+++++. No elaboration necessary.
2) Ease of Use. C. The switches that control which signal gets routed to the XLR and 1/4" (aka AMP/TUNER) outs are easily tripped accidentally. You MUST match the impedance correctly coming in (and you should be doing this anyway); it makes a HUGE difference w/ the Felix. If you have any experience w/ professional audio you'll be fine, but there is a learning curve.
While there is definitely a learning curve and it takes time to become familiar with the control layout on the rear pannel, it's well worth the effort.
If I had to make improvements, I would add or change the following:
1) An HPF filter AND Notch filter per channel. I don't like how you can only use one or the other per channel. For those blending a mic and a piezo or similar it would be nice to ditch some unnecessary low rumble while still being able to notch out the inevitable problem frequency,
While it would be great to have dual notch and HPF's it's always a
trade off isn't it. To add those features the Felix would have to be either longer or the control knobs would be significantly smaller.
3) If you're going to have this much tonal control, why not go one step further and add another fully parametric mid-range band on both channels? If simple is your thing, the Grace Felix probably isn't. Might as well have it all.
The Felix only has so much real estate on it's control surfaces. All it needs is an on/off switch IMHO.
Ric
DK