It does what I expect it to do and that is merging 4 midi signal to one. It requires usb power.
I have midi clock running trough 4 midi equipment with short midi cables. The fourth midi equipment have always reseived signals clearly. I put this merge box to add keyboard midi for the fourth equipment. This way the fourh equipment on chain receives midi clock and keyboard midi.
The signal chain is one equipment longer than adivised, but everything has worked fine with other equipments. Miditech 4merge has crashed 3 times. Result has been horrific. When it crash it mix all kinds of midi signals, including erase commands to few equipment behind it. And of course, the synth is screaming weird stuff. After power boot, it works fine again.
So if you by this one, it seems to work fine if midi signal chain is not too long. If it is more than 3 equipment, you better forget this product. I still use this product, but in other section of midi chain and it works fine now.
EDIT:Had to come back and change the review. This box is constantly failing. I used this box between Arturia Keystep, extra keyboard and Novation Laptop. This box cannot be used in live situations as it randomly goes to mode where it creates it's own midi signals and changes the ones you play. You have to boot it and then send "all notes of" to clear synths from creating weird noises. And this happens now with short midi cables. Weird as I have Miditech midi splitter/filther and it has never failed. This box can really ruin your show in worst kind of way. But I'm not sure if this is just a faulty unit that I have here.