I'd keep it. People can subscribe to both, and I often find myself looking for goods in EU stores (aka. not UK, sadly) so I don't have to pay ~30€ handling fee + tax. I know that OSS exists, but it's rarely apparent whether any given online store uses it.
This is true. !buyeuropean@feddit.uk is for whole Europe and not just EU (the community logo is bit misleading atm).
It's of course ok to have a more EU specific community but I personally think Lemmy isn't big enough to have so much fragmentation and incredibly specific communities (yet).
But we can link to !buyfromeu@feddit.org from our community if OP decides that there is need for EU specific buy-community. Fediverse is free and both communities share the same goal: support closer economies!