Thanks Eugenia. The Raynox does have "HD" in the name, for what that's worth.

raynox.co.jp/comparison/video/comp_hv20.htm#dcr6600pro

I chose this one after reading a thread on hv20.com about how the Canon model suffered from more barrel distortion.

hv20.com/showthread.php?t=441&highlight=raynox+comparison&page=7

imagometrics.com/FLReviews/HV20_Wide.htm

No doubt there are engineering trade-offs at play here. I think any loss of sharpness is quite subtle. The difference in my first two videos I think is largely down to the lack of a lens hood -- the wide angle adaptor seems to suffer badly from light entering it from the wrong angles!

"There is a reason why Canon's wide-angle adapter is so heavy..." and this reason is?

If there's a difference it's super minor. I can't tell if there is one between the first "with raynox" and "without" or if it just looks better because there is no glare on the box. :)