It was launched in September 1997 for use on both the MTR and the KCR and now is the most widely used electronic cash system for transactions in Hong Kong as many retailers are fitted with readers . It was launched in September 1997 for use on the MTR ( and KCR , now operated by MTR ) and now is the most widely used electronic cash system for transactions in Hong Kong as many retailers ( including supermarkets and fast food outlets ) are fitted with readers .