I have booked last minute domestic flights on Vietnam air twice, including recently for travel tomorrow. Both times the flight was around 50 or 60 USD, and the Vietjet flight was 20-40 USD. I actively avoid Vietjet. I have no problem with discount airlines, in the past year I’ve flown Wow over the Atlantic, AirAsia from HNL to KUL, and many others. But, the reviews on Vietjet say they often sell tickets for dummy flights that don’t exist, only to “cancel” the flight a day or two in advance, and reschedule the passenger onto a flight that may leave 12 hours earlier/later.

My advice for flying in Vietnam is to stick with Vietnam Airlines. It may be a bit more expensive, but it is worth it unless you are so flexible you can handle your flight time being radically changed.