Behringer UMC404HD

4 channel input/output USB Audio interface that is cheap in price but quite nice in quality, additionally it is plug and play for Linux (tested with Ubuntu 20.04).

The good:
The microphone inputs are quite clean, at least when using condenser microphones with phantom power (slightly more noise than in a SSL2 interface).
The headphone output has more than enough power to drive 250 Ohm headphones (tested Beyer Dynamic DT 990 Pro and DT 297 PV)
The knobs feel really nice, time will tell, but they feel a grade above the ones used in other Behringer consoles.

The quirks:
When monitoring, you can mix the inputs and the outputs with the MIX knob.
For the inputs you can listen to all of them at the same time, and stereo mix them as well by pressing the Stereo/Mono button.
However when monitoring the outputs for channels 3-4 (by depressing the Monitor A/B button) they are completely separated from the rest, including the inputs.

The less good:
The CLIP and SIG LEDs are useful guides, but you need to monitor your levels through software to set the microphones gain (at least until you know how they behave with the interface).
Line level inputs start distorting before clipping, make sure your signals are not too hot (even though they are not clipping distortion will happen), this seems to be more evident at higher frequencies.

The bad:
The line outputs are low, if you are connecting to a pro line level you might find the output insufficient, if you are connecting it to a PA or a mixer down the line, make sure you can pick something with a -10dB option for the level (and even then they might be a bit on the low side with the MAIN OUT at maximum level).

Overall the price leaves little to complain about.

The UMC404HD works perfectly as advertised, so no complaints. Plenty of separate outputs to route, which is a good thing (another headphone out would have been nice, but that's an afterthought, and wasn't in the specs).

The only issue that I have is a personal one, which is subjective as a matter of taste: I don't like the sound of the MIDAS preamps. They made my guitars all sound muddy, so I found myself EQ'ing more than I should. Many others seem to like these preamps, so I'm sure it must be a personal thing.

Aside the above subjective issue, I think this is a very good audio interface for the price.

I hesitated when buying this interface for a very long time. It was a toss up between the Steinberg UR44 and the Behringer UMC404HD. Both have the same sampling rate and bit depth options (which I wanted as a choice for mastering work in case a client sent in a 192kHz/24bit mix).

I choose the Behringer in the end because of a large number of reviews I read online and the price-tag. The reviews all boasted that it was just as good as interfaces that we're twice the price and more. That the preamps were top quality, etc, etc.

To my surprise I think that while this is a ridiculously good product for the price, its not as good as people are saying. Basically it comes down to little things that bothered me but may not annoy another user. For instance there was no driver/software for Macs so all I/O has to configured either inside your DAW or through Apple's own audio settings. Thats fine but I feel like you're potentially limited to the settings of the DAW you would be using regardless of the interfaces features.

Another little pedantic (i understand a lot of my issues with this interface are pedantic) problem I had with this interface was the how flimsy and light the product feels. Particularly the XLR/TRS inputs on the front.

However, saying all that, the sound is great! the preamps are really transparent and with the 24bit depth the noise floor is barely heard.

Also the AD/DA converter chip in the interface (which I found it very hard to find information on before buying) is really clean and I've yet to hear an artifact added to the sound.

All in all I'm pretty happy with the product and its ticking all the boxes...I just wish it was a bit more versatile on the software end of things and a bit more durable feeling (however saying that I've had not issues with durability yet, it just feels flimsy).