I would rather chance used OEM discs than Chinese ones.
If you have any issues at all with Chinese ones that's when your troubles will begin.
Postage will take 3 weeks minimum either way, you'll have issues with correspondence, and good luck if they don't fancy being helpful.
They could also be of a very low quality so it's false economy in my opinion.
Discs and shocks are unfortunately the most expensive parts on these bikes, but no point in cutting corners 'cos it could really go against you.
You can probably get a pair of Ferodo discs for a couple of hundred quid if you shop about.