Wow! Small but mighty
This is probably the easiest audio recommendation I've ever made: if you're curious enough about this thing to be reading reviews, just buy it. It's a shining reminder that significant audio improvements don't need to be fiddly, inconvenient, or expensive. I've tried all sorts of portable amps and DAC/amp hybrids. The CEntrance absoutely smokes the Dragonfly Red and similar flash drive-style units. Don't even get me started on the Schiit Fulla 2, which I found much worse than my headphone jack for everything but raw volume. Obviously it's not a strictly apples to apples comparison, but this also sounds better than the venerable O2 amp by a significant margin.
This thing is really in a league of its own. In my experience, Class A amps just sound better, so that's most likely the secret sauce here. I'm not prepared to claim I can hear a difference between DAC chips that can't be explained by simple volume difference, but I can generally hear the difference between Class A and Class AB amps. (Not claiming I could go 10/10 in a blind listening test, though!) Of course, the CEntrance doesn't deliver the skull-splitting power of a desktop amp with a dedicated power supply—I have the cult classic Gustard H10 on my desk at work, and obviously that has more gain. But I only buy efficient headphones that don't strictly need an amp, so power beyond what the CEntrance provides is wasted on me. For me, this is damn near perfect, and certainly close enough to perfect to get a five-star review.
Are there things I don't like? Yes, but only two. One, the branding on the unit is overkill and ugly. I keep it with the blank side up so I don't have to be reminded of what it is and who makes it 1000 times a day. Two, I have to remember to unplug my headphones before I plug in or unplug the CEntrance, because otherwise there's a significant pop in the headphones, which feels kind of rough even if it's not actually damaging the drivers. If you have any experience with Class A amps, the heat the CEntrance generates is perfectly normal. It's not going to burn your hands or burn down your home.
To end on one final positive note: I really appreciate the removable cable. My work and personal computers only have USB-C, so I bought a USB-C to micro-USB cable to save myself from hunting for an adapter whenever I want to use the amp. In short, this is an awesome and affordable upgrade to any mobile listening setup and I highly recommend it.
Would recommend to a friend.