I am interested in purchasing a teleconverter for my Sony HDRFX1, and am curious if anyone has had experience using cheap teleconverters like this Bower 72mm 2x:http://cgi.ebay.com/72mm-2-0X-Teleconverte...93%3A1|294%3A50
or this more expensive Raynox 72mm 1.8x:http://raynox.co.jp/english/video/hdp9000ex/index.htm
Specifically, I would like to know what specific problems may occur when using a cheap teleconverter other than the obvious consequences of teleconverters (vignetting and increased camera shake). What quality issues are involved with using cheap teleconverters? Advice from someone who has used one would be great. I want to know what my footage will look like with a cheap converter and whether it will still be worth it. I am going to use it for filming shots to go in a showreel on Vimeo, so although I will be filming in 1080p, I will only (or primarily) be showing the footage in 720p flash on Vimeo. I need higher magnification, but probably can't afford an expensive converter.
Any help would be greatly appreciated.