I would say it'd be worth a try-I have bought Addi needles on Ebay (from another seller) and have been very happy with them. I don't know if they are knock-offs or not, but they seemed genuine (in package, looked and knit like my other Addis).
I would say try it- if you only get one or maybe two the first time then you can check them out for yourself and if they are up to par-great! If not, you aren't out too much $$
Just my 2 cents. Good luck deciding!