More than 650,000 Koreans have opened Individual Savings Accounts over the past week since the tax-efficient scheme was launched March 14.

According to the Korea Financial Investment Association on Sunday, the number of people who subscribed to an ISA account was 658,040 as of Friday and their combined deposits exceeded 320 billion won ($280 million).

Even though the daily subscriptions slowed down day by day, the average subscription amount surged from 340,000 won to 490,000 won. Cash ISAs made up 94 percent of the accounts.

After excessive marketing activities aimed at increasing subscription, experts say, financial companies are now focusing more on attracting “real” investors.

ISAs allow customers to hold diverse financial products, such as cash deposits, funds and stock investments, in a single account with tax exemptions of up to five years on their financial gains.

The Korean version benchmarked U.K.’s popular tax-free saving device with the same name.