Ive used their ticket system once and it wasn't blistering fast, but they did respond within a day. Ive used their telephone service a few times, usually have to hold for about 10mins and if they cant assist there and then they call back.
As regard to reporting bugs, Ive found them quite responsive although perhaps not as quick as TPlink when it comes to realising updated f/w (they usually send a beta through quite soon before general release). They seems to be sticking a bit in the mud though about my request to increase telnet sessions
Has anyone actually had any hardware repaired by Zyxel in the UK?
No sorry - not had to RMA anything and my contacting them has always been around f/w issues.