Yes, it is generally safe to pay via "FPS QR Pay". When you use the function via EleBanking app, banking app will ask you to verify your transaction using Two-Factor Authentication / Mobile One-Time-Password, to make sure the transactions are properly authorised.
EleBank Causeway Bay Physical Store
Address: Shop S & X, Hong Kong Mansion, 1A-1L Yee Wo Street, Causeway Bay (Exit E of Causeway Bay Station)
Opening hours: Monday to Sunday - 10am to 9pm (The Physical Store's opening hours may be adjusted on certain public holidays. Please refer to the Bank's announcements.)