It's a great little unit that works as advertised. Using AAA batteries is for me an advantage compared to 9V batteries, and it works well with NiMH rechargables, and is very compact and appear sturdy.
The sound is quite clean and is possibly a bit better than e.g. the built-in headphone amp in some of my keyboards (running line to the stick and then to the in-ears sounds more open than plugging the in-ears directly into the keyboard).
It takes either a balanced mono signal or an unbalanced stereo signal in either jack or XLR form. It has two internal switches: stereo-mono mode and high-low, which essentially attenuates the output 6 dB for use when your in-ears are sensitive (I run mine with Shure SE-425 and use the low setting).
It has a hard limiter built into the input, so as soon as you go just a bit above line level, it kicks in and sounds pretty distorted -- but it also helps to protect your ears somewhat from too loud feedback noises... Just make sure your normal listening levels at the input are around line level, so that any feedback will trigger the limiter.
I use it mainly for live playing, but it also works just fine when e.g. practicing bass at home: Just plug in the instrument directly in the jack, and there's enough gain to give you a full bass sound in the in-ears.
The only slightly negative is the gain knob, which initially is very sensitive (small adjustments gives a large increase in gain) but then the difference becomes smaller. It's almost like the going from 1 to 2 equals the difference between 5 and 10 (assuming 10 would be full scale).
