I use the M-Scaler with the Hugo2 and the Dave. You've probably figured it out by now, but the M-Scaler really isn't about frequency response, it's about coherence. It brings the music and the acoustic ambience together something fierce. I did NOT want to spend the $5k for the thing, but I find it really hard to listen to either the Dave or the Hugo2 without it now.
So in evaluating it, I'd recommend not listening for specific detail-y things like bass or highs or whatever, but rather by just sitting back and seeing whether you enjoy the music listening experience more with or without it.
I knew I had to keep the thing when I found myself still in my chair having to badly go to the bathroom after hours of listening, but not being able to leave the music. I also know because all I have to do is hit the bypass and I immediately am less engaged with the music.
Anyway, will be curious what your experience is. Good luck!