flame tank is a good unit but it can change a war with only one front I usssualy fight wars with multiple fronts if you use it in one front it would be less efective it specialy effective against bot nations as they mostly have un armoured units
you can use the flame tank with some high damage units to have a pack a punch unit because in late game ussualy we have moterized and infantry the most so this formation 2-4 flame tanks and heavy \ medium tanks 4-7
