Good esim, stable connection, unlimited package is cheaper than buying a physical sim at the airport, the procedure is quicker. At the airport in Vietnam, there is wifi, so you should activate the esim first so that when you go to Thailand, you can use 4G immediately. If you already have an esim in your phone, you should disconnect the existing esim first and then add a new esim to avoid errors with your original esim. Activation is quite simple, read the instructions carefully and you can activate it.