Anyone know anything about disc brakes?

I could, but I don't like buying things of that value from China - up to £20 fine, if something goes wrong, I'll live with it. At around £50, i've had too many things I've wanted to return / got into awkward convos in broken in english to want to do it again...

Also that's still £20 quid more and 6 weeks of sitting waiting and wishing.

I bought a seatpost last year that was undersized, the refund is still "pending" and I've not worked out how to actually escalate it beyond the seller, who simply says it's up to Aliexpress now...