Usually, no one knows how to use or what is MST. I will lean over with my phone, then when the card details are into the terminal, I just tell them to charge that card. At least for these terminals where the first action is to swipe the card (as opposed to like SP power where they need to key amount first).
SP utility, I used to always go to Toa Payoh to pay using Samsung Pay MST. After so many times, the most of the cashiers there know the drill well already. Now with the app, don't have to physically go down anymore, unless one is looking for Grab card on the Samsung pay app. Samsung Pay points don't justify the extra trip down to make payment for me. App is so much more convenient.