Apart from paper cards which I think is most commonly used method to store passphrase the need for steel cards only arises when you are not confident about paper. I personally prefer using paper and have already laminated and stored it safely.
There is a new project that I found out on another forum that uses steel but has a very unique way of storing it. You can know more about it on their website.
There is a new project that I found out on another forum that uses steel but has a very unique way of storing it. You can know more about it on their website.
I designed and manufactured the product you cited, happy to answer any questions you or anyone may have about it!