Doesn't this do the same as unicon?
In a way, yes, Unicon and Galaxy Icon Themer do the same thing - that is give the ability to change icons but the difference are:
Unicon
- is a paid app
- uses Xposed framework to do the theming
- has icon masking support
Galaxy Icon Themer
- is free
- uses Touchwiz native theme engine to theme icons
- no icon masking support
Galaxy Icon Themer Pro
- is a paid app
- uses Touchwiz native theme engine to theme icons
- with icon masking support
- with Per App icon theming with several options and also is in continued development