It improves brightness control more than Apple's way. 
Traditionally, the iMac product line have a dark gamma value less than windows or TV. This application can adjust brightness easily dim or bright.
**** I recommend you Brighter-Screen Lite if you don't have a big-screen mac and don't use mac for watching movie often.
1. Maximum brightness 105%
2. Minimum brightness 10%
3. Movie mode
∙ it is same as photoshop shadow effect and useful when you watching high quality movie on fullscreen.
Tip 1. Default short keys
∙ More F2 (or Fn + F2)
∙ Less F1 (or Fn + F1)
(These are 2 times faster than apple's buttons.)
Tip 2. Sleep Display
∙ Display sleeps below 10% brightness level to save energy automatically.