I got this little mixer so I could hook up a computer and an Echo Dot to the same set of external speakers. And it works exactly as desired.
Setup was a breeze: use 1/8" minijacks to plug into the mixer's inputs, run a 1/8" minijack from the mixer's output to the powered speakers, plug in a USB power cable, and set the audio levels on the mixer.
I originally had the mixer's USB power cable connected to a powered USB hub, but heavy USB traffic would cause the mixer to intermittently emit pops and snaps on the output channel to my speakers. Got annoying real fast... Issue was resolved by plugging the mixer's USB power cable into a dedicated USB power adapter.
I haven't tried running the mixer on batteries, so can't comment about that feature.
The blue LED power light is quite bright. You can cover it with masking tape or electrical tape to cut down on its intensity.
This little mixer has been running 24/7 for four months now, and it hasn't given me any trouble. I'm not using it to its full potential -- regularly turning knobs and mixing audio levels -- but I don't need to. I wanted a set-it-and-forget-it device, and it's working like a champ.

Nice simple and extremely lightweight device. Sliders and dials are easy to use. For simple podcasts where you want to monitor your own mic, as well as your guests from the computer, works fine. But be warned you need clean power to it. Either 1) supplied batteries or 2) USB power direct to the wall. Do not power off your computer as the "dirty electricity" presents itself as a high-pitched squeal on the device. USB direct from the wall is fine (minor feedback) if it's clean power. Batteries are the best and have the least amount of feedback through the device. I use this with input 1/2 being off my H4N which connects to an XLR mic, and input 3/4 being the audio out from my PC, which monitors a Hangout call.

For cost of the device and purpose, it gets the job done. Wouldn't suggest it for professional work though.

I wanted to find a way to plug in both my Samsung smartphone audio with my laptop audio into the same desk computer speakers. I work at home frequently and like to listen to music from my phone while I work but sometimes need to listen to audio from my computer; I needed a solution where I could listen to both (not simultaneously) without having to constantly plug/un-plug audio connections to my one set of computer speakers on my desk. This mixer works well for it! It was simple to hook all the devices together (make sure you have enough audio cables: device #1 to mixer, device #2 to mixer, mixer output to speakers) and just adjust the Master slide/dial (far right on the picture) to the right level. Highly recommend for a setup like mine (i.e., two audio devices into one set of speakers).

Fantastic idea, terribly executed. I really wanted to like this item. But the level of noise produced by this device makes it totally unusable for most applications.

There is a tremendous amount of noise when running on battery (2xAAA) power, and the noise persists, but is slightly less when running on USB power. The minimum amount of noise I experienced was when using a USB battery back to power this. Having it plugged into any other USB power source (wall plug, computer) produces an unacceptable level of noise.

I give it one star because it is not even useful for its primary function. The size and portability are awesome, but it just does not work as a mixer.

I am keeping it to use for Ham Radio applications, where some noise is acceptable, but unfortunately it is unusable on a daily basis.

Also, the price is way out of whack. If this were $20 I may have given a more favorable review, but for $40 one can buy a decent Behringer mixer that will perform much better (albeit on 120v power).

I bought this to put on output of a guitar pedalboard. The background hiss (or noise floor) was too high. When plugged into my powered speaker with volume on speaker turned up high, there was a noticeable increase in hiss (white noise) when the mixer's master was turned up. Bottom line..The mixer has noisy preamps. I ended up getting a small battery powered Behringer mixer with very quiet XENYX preamps. If you will be running your speaker amp at higher volumes and have quite passages in your music (or music is very dynamic), look elsewhere. If you are playing louder overly compressed type music thru the mixer with your speaker amplifier turned down to normal to lower volumes, it may pass. Bottom line.. it can not be used as a pro (or semi pro) type mixer. It's not quite enough. It may work if used in noisy places. But if you are picky, pass on this one.