The .7x is sharp and introduces very little distortion. Likewise, the .6x. The fisheye provides a vignetted image and lots of distortion, which makes it a great effects lens. It provides about the same coverage as a 19mm lens on a 35mm still camera. The Century adapters are certainly a cut above the converters available at most camera shops, and are priced accordingly.
Century does a line of optical converters for the more compact cameras too.
The range is similar to the Canon adapters, but the prices are a little less. This passive device is much quieter than powered systems like Canon's MA-100 XLR adapter. DXA's are now available for a variety of cameras, including Sony, Panasonic and Canon. Famous for their range of microphone windscreens, Light Wave Systems has just introduced a couple of interesting products for the Canon XL1. A secondary benefit of the SI is to move the eyepiece about two-inches further forward, which helps to improve the camera's balance.