I bought these pens based on other reviews, but am wholly unimpressed.
These pens don't work on the DVDs I'm using - and I don't just mean they take a while to dry, they don't work at all. I'm using blank DVDs with a 'label layer' on the upper surface that usually makes them easier to write on (something like: TDK DVD+R 16x 25pc Cakebox (T19443) ).
Perhaps these pens work on the totally blank/shiny disc surfaces, but not on those I've tried. Be careful.