I ordered a different case from that seller for a relative. I had a free trial of Prime, ordered it on a Saturday afternoon and it arrived at around 12pm on the Sunday. From that I figured that they must be dispatching from within the UK and in any case, it does say fulfilled by Amazon so anything that says that should be safe.
The link directs me to the Amazon.co.uk site as I’m also in the UK. With the case not yet released, it’s possible that it will drop in price between now and release, taking it below the threshold for import VAT in any case.
I spotted their website and i’ve emailed them. It’s not showing on their site yet.