What about Japan? AFAIK the yen is not subdivided into lesser units, nor is it a subdivision of a larger unit. Even if denominations are issued in multiples of 10**n yen, that is arbitrary and doesn't fundamentally make the yen a decimal currency.
The Wikipedia article Non-decimal currency explains the situation in full:
Today, only two countries have non-decimal currencies: Mauritania, where 1 ouguiya = 5 khoums, and Madagascar, where 1 ariary = 5 iraimbilanja. However, these are only theoretically non-decimal, as in both cases the value of the main unit is so low that the sub-units are too small ...
The word you're looking for is not "metric" but "decimal".
Pretty much all currencies are decimal these days except for currencies that have divisions where the sub-unit is no longer used as it's worth so little.
The only countries left with non-decimal currencies are Mauritania and Madagascar according to wikipedia
So a few things to talk about re: your question:
1. Be wary of articles like that
There's a ton of them, and although they all look to be legitimately comparing pros and cons, make no mistake that they are collecting commissions. Often they collect commission or referral fees from both so it doesn't matter which you choose.
It doesn't mean that there isn'...