It's been several months since I've used it but I would have used it over Unity's default Shuriken particle system if it wasn't for a few bugs I was running into getting it to trigger via script when I wanted. At the time it had several features that Shuriken didn't that made it pretty desirable. Things like noise fields, trails, sampling color from a texture, emitting from skinned meshes, (lights? I can't remember) etc. Unity has been upping its game by upgrading its particle system and now has things like noise, trails and lights, as well as making it easier to access things from scripts. Since then though I've kind of skipped over Particle Playground and went for PopcornFX (does a lot more, but also much steeper learning curve, and not as friendly to use with Unity). To sum it up, it's a nice upgrade to Unity's particle system adding additional features that I enjoyed using. Very quick to pick up, especially if you are already familiar with Unity's. Developer was quick to respond to my bug reports as well.