you can’t use gold or silver, because those aren’t readily available and 100% useful. an angel gold tag may be a LP store currency, but because there is not enough information to say it’s A - pure gold or B - 0.1 M3 exactly (probably rounded up so it actually takes up space in a cargo-hold).
this wasn’t the point, plex conversions aren’t a linear exchange.
though +1 for the Koku alternative.