You can find some information here:
https://www.bitcoinsuisse.ch/assets/pdf/BTCS_CertificateHowTo.pdfI was fortunate to buy a few both funded and unfunded, and they are really really nice. I've even redeemed a few and they were in tact
I have no idea whether they sold the number they quote in that document.
I took a few pictures of one of my unfunded certificates. They are a heavier material, not sure what but it doesn't feel quite like paper, with embossing and a small hologram. Very sharp printing that's held up nicely, though I keep mine in sleeves. To redeem there is a private key concealed beneath a scratch away surface that is beneath a perforated section you need to tear away. My experience has been that the QR code for the private key is impossible to scan with a phone, but the private key is quite legible.
I think they were a bit of a hidden gem that slipped away before most folks were aware of them.. I'd buy a new issue but I don't think they have sold them or stated plans to sell them in years..