I got a joytech one for a tenner a while back. Much better than composite, and slightly better than RGB scart. How good the interlaced picture looks on your TV may also be down to how good the de-interlacer on your TV is, if it does that kind of thing, I know many of the modern LCD sets do all sorts of 'processing' to the images.
The biggest difference for me is progressive display which is nice but no colour bleeding at all. the lines are crisp (although jaggy). The ar jaggy because it's a relatively low res on a large screen.
One thing though I find going from composite to component is a kinda 'mmm, improvement is OK, cheers' kind of deal, but going from component to a composite input is more a kind of 'what the heck is this fuzzy crap you call a picture?' sort of affair.