itch.io

Yes, the addon is required to make Effekseer files work in Godot.
However, the way I make the animations in Effekseer won't make it work in Godot 3.x. (https://effekseer.github.io/Help_Godot/v3/en/introduction.html  => "Known Issues" => "Advanced rendering panel function does not work"
It seems the issue is not there in Godot 4.x.

It should work in Godot 4.x then. Tell me if you're planning to use Godot 4.x and I will run tests before you buy anything