This product is absolutely spectacular and as far as portable amps go it does a phenomenal job with my headphones. There was a factory defect with my first pair and Bloom did an exceptional job of replacing it, and I have never been happier with an audio product..

Coming from the orginal ifi go blu paired with my hd6xx this is a game changer.
I listen almost exclusively in bluetooth mode, as LDAC sounds as good as a wired connection to me and I like feeling untethered.
I always had a feeling I am not getting the most dynamics out of my hd6xx with the ifi go blu although it does reach satisfying SPL levels.
By contrast, the Cayin RU9 can push 4 times as much power through the hd6xx drivers in hyper mode (minimum 20watt usb port). I was pleasantly surprised with the greater flexibility and ease I was granted in eq'ing the hd6xx to my preference without reaching the limit of distortion. Having greater flexibility in tonal control with the classic, modern, and class A modes is nice, though I tend to leave it in classic mode.
I recall tube rolling genelex gold lions into an old little dot amp, and the gooey tube character was very apparent and charming, if syrupy. The Cayin RU9 does not reach the full-fledged gooey tube nature like that amp. But it does introduce just enough tube character to keep things interesting, without generating significant heat like traditional tubes.
If I had to detract anything from this device, it's that I am not finding great use for the magsafe compatibility, bluetooth range is not as good as the ifi go blu, and that the battery life could be better. In terms of battery life, best case is I can get 4 hours in medium gain listening at medium to high levels. At the same time, I don't leave the house with this dac so I am always near a power source. To me, the Cayin RU9 is portable in the sense that I can take it from the living room to the dining room.
My suggestion for those considering this is you have two options if sleekness, power, and bluetooth are your priority, this or the ifi gryphon which has equivalent power output into 300ohm, without necessitating auxillary power. I wanted a departure from ifi, and I was curious about how Cayin implemented the nutubes into this hybrid dac. For my use case, 5/5

This is a pretty unique piece of equipment. Between the tubes and hybrid mode, as well as the magnetic features, this little amp/DAC is kind of a category of its own.

As the reviews point out, you do get three different sound signature qualities. A warmer tube sound, a more neutral solid state sound, and a hybrid mix in between. The size of the unit is very portable size wise, and with the magnetic back, this little unit will stick to your phone and not move out of place. It's game changing. I'm using this with a pixel 9 pro, but with a peak design everyday case which adds the magnetic feature.

There is one one negative, and that is the battery life is not very long. 3 to 4 hours maybe. But, there are some really affordable magnetic back batteries on Amazon that have been suggested in some audio file communities. The Lisen Brand 5000 mAh battery on Amazon works seamlessly with this. Yes now your rig is a little thicker, but you have double the battery life. Not always needed though. So that kind of helps that negative not hit so hard.

Fantastic sound, adjustable on three modes, which I change depending on genre sometimes - and they each can make the monarch Mark IV really sing.

The second negative is the Bluetooth antenna is extremely weak. Your phone has to be very close for this to even work. I mean it's good the feature is there but they really should have engineered it better. Using a USBC Bluetooth dongle which gives you other codecs, the reception is slightly better. Enough to walk around with the whole setup. But ultimately it's still not ideal.

Five stars if they give it a little bit more battery life and fix the power of the Bluetooth transmission. But even with these negatives it's still four stars because of what it does overall.

Very nice sounding dac amp with three modes. Awesome unit! Bloom Audio is a great company to work with.

Phenomenal service as always from the Bloom team! I did not end up keeping the product but an exchange was done literally the same day.