I don't see why "cheapest, fastest, most secure" is not enough? I have saved hundreds of dollars in fees.
Say i buy an Oz. of gold from Amagi (or whoever). It is $1350.58 if I used a credit card. If I instead use bitcoin I pay only $1311.37.
If I pay with a credit card the seller has to wait for verification to send with confidence. If I pay with bitcoin the money is theirs within an hour and they know it can't be clawed back.
If I pay with credit card I must expose all the information needed to steal from me. If I pay with BTC the seller does not even know who paid. Which is no big deal for them.
cheap? I pay ZERO fees when I am using my card, it's instant and "secure" enough (nothing is secure on internet).
the seller doesn't have to wait. if it's a merchant, he can get the money from bank same day or next day.
yes, you "expose" the information BUT you can make chargeback while with bitcoin you can say "bye bye" to your funds.
BTC wasn't made as a payment system. first, it's limited as volume of coins and second, it's hard to be understood by the normal people.
You may think you are not paying for the Tx, but Visa is not a charity and someone MUST pay. Assuming you don't fall for their debt traps then the fees are paid by the seller who raises prices accordingly. As a business owner I assure you that your purchase is far from instantaneous. It typically takes days to weeks to receive a settlement and sometimes takes months.
The problem is still why it should be better for the merchant, not the seller. I imagine most of the merchants would need to convert the bitcoins back to fiat, and that would have a fee, which could be higher than visa's or mastercard's fee. On the other hand it would be profitable if the merchant is able to buy the products he sells directly in bitcoins.
Most of the businesses I have helped to accept BTC have gone with a payment processor like BitPay. They take 1% as a fee, which is 1/3 the cost of a visa Tx.
Just checked the website. No discount for BTC, I call shenanigans

And Amagi Metals is known for shady business practices (quick bitcointalk search shows this
https://bitcointalk.org/index.php?topic=1456781.0 as second result), so you buy with $1311.37 worth of BTC & get a brick in the mail 3 months later, SFYL. With CC? No prob, get your money back

I'm not sure what you are looking at? They most certainly do offer a discount for cash sales, including bitcoin. I have bought as much as 10oz. at a time and saved thousands. This is also true at Overstock and most retailers who take bitcoin. Check again.