I'm using them, they seem fine. The quality of my 42" HD TV seems very good w/the wii, but I never tried it with the composite inputs.
In general, "different" quality of cables is very minimal; 90% of the BS around stereo equipment (around cables) is voodoo; test after test shows there is no difference between cheap, noname cables vs. the more expensive ones such as Monster, etc.
The build quality of the cables seems OK, certainly on par with the nintendo ones.
I'd buy them again.