What a great little device. An absolute must have for any GameCube enthusiast. It's a hugely noticeable improvement over the standard AV output in terms of sound and picture quality - especially if you're playing on a larger screen. I've been using it for around a month now don't imagine I'll ever go back to AV.
Only minor criticism is that it sticks out quite far behind the GameCube. In the end I bought a 90° angler for the HDMI so that I could push the GameCube back without putting strain on the cable/socket. This just redirects the cable so that it points downwards rather than outward. Otherwise, no complaints.