Frankly, this app barely rates two stars, but it is up front about what it does and actually delivers on its modest promises, so it defensibly earns a three. There are a lot of shortcomings, not the least of which are the total lack of customizability, sound, and worthwhile graphics. Forget HD, this is barely SD. The demo images represent the best possible view of the app; your mileage may vary considerably.
That said, the app description is accurate and truthful; for an app that wasn't originally designed to stand in its own, it's not bas, and it doesn't pretend to be a top shelf app.
If you're looking for an app that lets you play with fireworks by mixing and matching, this isn't your app. Go get FireCraft or something. For those who just want a quick fireworks show to superimpose over a photo, then go ahead and get this. Just make sure that the photo you choose is dark; even dusk photos are generally too bright.