seen alot of these but not that model on ebay.
flashed using serial?
it's currently the only way.
the EX3510 isn't supported here, btw.
shipping to UK costs more than the router itself. 
oh, I see they removed the fixed UK shipping price they previously had listed on the web site.
the high price might be because they have to pay the customs etc in advance for you.
check what I'd cost you to ship it from SE to UK.
I can send you one of mine, and you buy me a new one from them.
you could also reach out to @alright seems you're looking for the same thing, perhaps you could co-buy ?
that would be great If I could get it in either of these countries
USA
UK
Saudia Arabia
UAE.
Shipping to any of these will be easier for me, in that order.