Peter,
For some time now, where possible, I have been ordering PDFs as they are direct digital copies of the paper certificate (at £9.25) that would otherwise come through the post - but subject to the following (GRO Q&A) caveat:
"Q4. Is a PDF the same as a certificate and can I use a PDF as evidence for official purposes, such as a passport application, or if giving notice of marriage etc.?
No. A PDF is not a certificate. A PDF will have no "evidential" value, and therefore a paper certified copy [certificate] is required for official purposes, e.g. if applying for a passport, driving licence, or where required to give notice of marriage."
Willyam
Ps - of course Wales won!