I had the same concern when I bought it, so I put the planet audio one on the bench and put a sine wave in from a calibrated sig generator, tested THD by comparing the input to the output with a dual channel scope. It is good 2 go. It's cheap because it's a closeout, they quit making them. Not many people need that many channels. List price was 250$ or so originally.
It is big, it is about 12"x 12", it's built in an amp chassis.