There have been loads of interesting comments and I’m grateful to everyone who has contributed. A couple of things to highlight:
You can get cheap and compatible tags on ebay which are much cheaper than the genuine proximity ones.
I’m reliably informed that these ones and I imagine others like them work fine with the panel. They are pretty cheap too so well worth a look. I’ve not tried them before but I’ll get some in to play with. I’ve always been a little unsure about them though, someone said to me once “well you wouldn’t write your alarm code on your keys” and this is a similar idea. However I think there is value for example if you want to give a tradesmen access for a few days and don’t want to have to set up a new code etc.
You can get much better voltage regulators than the one I bought. There’s been a lot of discussion in the comments but this one has been popular:
It is very hard to argue with the price, and it’s much smaller and neater than the one I used. I still find it incredible that you can get anything delivered direct from China for less than a dollar all in.
Thanks again for all your contributions, please keep them coming!