Each pack has about 5 themed tracks, each about 2min long. So I would say worth it for prototype or small game but not really enough content for a full game.

I'm not sure how much of ECS you can apply in that case... If you have something like game objects/entities then it might work/be useful.

Of course! ECS is Entity Component System. In short: separat your code into logic (=systems) and data (=components) attached to game objects (=entities). It enables you to add different behaviors to your game objects by composing different components together. An example: I have a system called RenderSpriteSystem which automatically renders every entity that has a PositionComponent and SpriteComponent attached.