As the article says, not very many. It's $200 (USD), and the average income of a North Korean is $100/month.
Traditionally (at least in the west), a wedding ring was meant to cost one month's wages.
A car typically costs around 6 month's wages (or more)
A house used to be 3 years' salary (though with mortgage bubbles, it's common for a mortgage to be anything up to 10x salary)
So, 2 months for the average DPRK citizen to be able to afford one of these? Makes it a pretty desirable object. Therefore, there will be many in NK who will want one of these, based purely on the price. So, in answer to "how many of them", clearly it's "as many as will want to save up"