Picked up 5x V3 mono amps off Kickstarter soon after I got 4 ohm speakers (Kef R Meta) because I suspected the Denon x4800h might not be able to drive them to loud volumes. Was proven correct, the Denon would go into protect mode and reset when I turned the volume up too loud. I turned off the internal amps and configured to pre-amp only, and put these monos between the receiver and speakers.
Turns out these amps are a nice upgrade as well as giving me headroom. The sound is very transparent and resolving, but also authoritative. Bass frequencies sound just as great as the rest of the FR. Where there's no sound, these are silent - no hiss. The Kef Meta speakers all sing and can sing loud without much if any change in sonic character on these amps.
-10db is about as loud as I pushed before deciding my ears are more important than stretching the legs on these amps, but they sounded just as good here as anywhere else on the volume control.
I use RCA, haven't yet heard ground loops or similar. I do using the 10A PS hear a funky sound if I turn one of the 2 amps paired on the power supply to off - this is true after the filter even, but only when it's manually switched to off (as opposed to Auto). I don't think measurements show much of a difference in 1 vs 2 power supplies.
If I did complain - the horizontal orientation takes up a lot of room on a rack, and the main heat sink connects to the bottom of the chassis. Mounting feet on one side and standing the amp up sideways gives a lot more room. I'd prefer they included feet that we stick on the amps rather than assume they'll sit horizontally. That said, the amps are LIGHT and if standing sideways, be prepared to stand them back up several times if you're moving them around or working with the wires. Not an issue when done, but annoying while working.
And if you do stand sideways - add rubber feet, and be sure there's some room for air flow.
But still - compared to what these cost? I have no real issues, and am blown away at the quality provided at this price point. Great stuff.