I bought this to split up my midi out to connect various machines in my studio.
As many machines don't come with a MIDI through option it's impossible to daisy chain them, so I needed a splitter to connect them to my one midi out on my soundcard.
This device can do other things like filtering certain MIDI data, but I haven't used those yet. (I'm relatively new to larger MIDI setups)
As a split-box it is easy to use, basically plug and play. Connect the input to your MIDI out and then connect your machines to the 4 outputs.
There's no need for a PSU as the box is powered via the MIDI out. (Apparently there are devices where this won't work, so you may want to check this first, but my guess is most will. Again - check!)
The box does feel a bit plastic-y, so while it's good for studio use and the occasional live performance, I'm not sure how well it would deal with heavy gigging/touring.
I also find the placement of the LED that shows incoming data next to the input - which many will want to have on the back like me, a bit unfortunate, as it's not very well visible.
Other than that no complaints. At the price this is a very useful, decent little box.