Mrs Gozza and I both got the card when we had ours done - I work for the NHS and had mine at work, Mrs G went to the local surgery. They're not really designed as proof you've had the vaccine, rather it's your record of what you had, and the batch number, if you later suffer side effects than mean your batch has to be traced.
The problems with using this card as proof of vaccine are:
1) you can buy blanks of this card on e-bay (or at least, convincing fakes), so having the card only really proves that you've got the card...
2) there's no real proof of who the card belongs to - sure, mine says "Paul Gozza" on it, but unless I also have some separate proof that that's my name, I could have borrowed, or stolen, it from anyone.
Having said that, until something else gets sorted, the card is what we have, and I'll be carrying mine just so I've got it if anyone ever challenges me, at a pub or shop doorway for example. But if I owned the pub or shop, one of these wouldn't convince me.