These experiments are fun.

Anything with moving parts, such as the cassette models, are more prone to data loss and are much more expensive. Etching / stamping kits are generally superior, with the caveat that they are more difficult to set up.

Alternatively you can skip the dedicated kits entirely and just pick up some stainless steel blank cards. Much cheaper and your purchasing history is more discrete. As they are the size of a credit card, you can carry one in your physical wallet if for whatever reason you needed to transport it in an emergency. Steel credit cards are quite common and would not be flagged in, say, an airport luggage search.