i was indeed surprised that there's no preview & multiview output when I first hear of the release... i guess it's more to target the consumer market and functions more like a seamless presentation switcher. However, with the built in scaler at the pricing point, it might just work very well as a submix HDMI switcher for a smaller but proper 4ch basic vision switcher.
I see the usefulness in the youtuber gaming review markets. 4x gaming screen feed into this ATEM Mini, plus 3 cams into another ATEM TVS. Total of 7x valid inputs on a super budget setup that works.