They provide high air flow in/out of your case, and still remain super silent whilst doing so.
I run mine between 700-1000 RPM, and I can't even hear them, unless I put my ear right next to it.
In the package you'll receive:
-3 rings (red, blue and white)
-Four Black screws
-A 12v-7V step down reducer
Overall, these fans are definitely worth it, and much better than my Fractal Fans that came with my Define R4.
Here's my unboxing and overview of them: