In general, I don't write formal lengthy reviews anymore... just stream of consciousness stuff, or short to-the-point comments which I like to hide in the middle of threads.
Rag is better than Mojo on a relative basis as follows: 1) More clarity. Hard to believe, but in comparison, Mojo has a low level veil or fog around the upper bass / lower mids; 2) Silkier, more slippery, more liquid treble. Mojo's treble sounds a bit staticky, jumpy, unrefined, grainy; Rag is the least grainy amp I have heard tube or SS; 3) Deeper more complex stage (both Mojo is more upfront and one dimensional), this openness to infinity, better sense of space; 4) Cleaner faster transients; better separation, layering - sort of this inter-instrument clarity; 6) Does not require one hour plus warmup like Mojo - Mojo can be aggressive when not warmed up. Rag is ready to go in five minutes; 7) Better reproduction of bass texture. Mojo has heavier bass; Rag bass is subdued, but slams just as hard when recording calls for it; 8) More resolving of low level information; also being able to differentiate tiny changes in volume. This last one of course will be heavily dependent upon rest of gear. Rag is the most resolving SS amp I've ever heard. The presentation of detail is also not in your face. It's subtle - real high resolution instead of bad photoshop oversharpening filter. The microdynamic capability and treble smoothness of the Rag makes it a very seductive listen.
Rag got super hot during recent heatwave of death last week where I live - volume knob was slightly uncomfortable. Now that things have cooled down, volume knob is warm but OK - no different from Mojo.
No hum. I use power isolation bricks. My Mojo hums without the power isolation bricks because I have LEDs, dimmers, ballasts, etc. all sort of crap in my house. I'll try the Rag without the power isolation bricks to see what happens.
With speakers the Rag is fantastic. I have three pairs right now. I designed all my speakers to be powered with low-power tube amps. I actually like the Rag just as much as the tube amps, but for different reasons. I tend prefer the Rag more with the ones on the lower efficiency dipoles and BLHs. I prefer the tube amp with the front horns. But honestly, just a slightly different sound - going back and forth every other day.