Output quality is limited by input quality. You can't improve a video signal with a magic black box.
If that device is using either RGB or Component output from the consoles, then it will be pretty good. If however it's taking S-Video or worse, Composite output, the resulting picture will be a dog's breakfast with all horrible colour bleeding and whatnot.
You're going to have to track down a review somewhere, or take the plunge and try one for yourself to know for certain.