I have a Hip Gear branded "System Selector" which looks remarkably similar only it has space for 5 inputs, composite & s-video. It's worked like a charm for years on an old Samsung CRT and, at least on the composite side, I've never noticed any negative effect on signal quality although, like Polygon, I haven't ran s-video through it. It was something like $10 from a local Blockbuster, found in one of those bins of random accessories.
Here's the one: http://www.estarland.com/DefaultPage.product.30696.html