Your MegaEsim connects to OOREDOO TN. It is the largest mobile network in the country and reaches close to 97 percent of where people live. That matters because you are not on some small backup signal. You are on the same towers locals use every day.
OOREDOO TN runs a strong 4G network across the populated parts of Tunisia. When you land and turn the eSIM on, your phone latches onto it on its own. You do not pick a network by hand.