Yup, all of these effects are optimized for 2D use right out of the box.
However, because unity is a 3d game engine, these effects can also be used in 3D. Although some VFX may need to be tweaked to better fit in a 3d environment.
Viewing post in Ultimate Cartoon VFX MEGA PACK - Unity Prefabs comments
Yup it does include the demo scene. But these are not png files. I'm glad you asked that.
These effects uses the Unity Particle System. So if you're not using the Unity Game Engine I don't recommend buying this.
If you are using Unity, then this package is a dramatically more lightweight, flexible, and efficient than using standard png files for effects.