I don't know what the difference would be, but I've never liked the cartons tbh, unless used for emergency use. DS has had a bottle of formula before bed since he was 6 months (Hipp follow on), when we went on hols I took a carton of ready made to the airport hotel and he spewed it all back up. It reminds me of UHT milk!
DS used to bring up entire feeds once or twice a day, every day for months. It was horrid

Could Caitlin be allergic to something in the milk?