I don't see how carts helped to expand the snack choices since the snacks are preloaded onto baskets stashed in the overhead bins. I do like the improvement though.
Each cart also has a holder for the tablet, so that when they do any sort of sales such as snack boxes, pillows, blankets, alcohol, etc, they can charge the card right on the spot, and it frees up the second crew member because in the past, one FA would have to hold the tub of items for sale, while another FA had to follow with the tablet and run back to the galley to resupply the tub.
I think it would be more efficient if they had one FA serving rows 1-10 front to back, while another FA served rows 11-20 front to back, while the third FA serves rows 21-25/27 from the rear galley for the A320, and do something similar for the A321. With the E190, they can simply just have one FA serve 1-12 and the other FA serve 13-25.