Channels seem to work pretty much as expected. Some reviewers mention that every output is mono and I can confirm this. Even if you play stereotracks in mp3 player and take it out from the rca-pairs it is all in mono.
MP3-player is fine, but there are some things I had to figure out. Plays only 16-bit wav files which is ok but good to know. Also the SD-side at least plays files in the order they are written on the card. I assume this is same in the usb-side but haven't tested. I don't think there's a way to program the player so it's good to know.
The "reverb" effect is actually a really short delay and basically useless, so don't buy this for it :) All dial knobs seems to come off when pulled, a feature I suppose.
For the price this is a handy way to sum mono inputs to few different outputs - I personally play backing tracks from the MP3 player and plug instruments to mono channels and take output from rec out to a separate mixer, so I don't know how the 80W outputs behave.