There are just different ways to root Galaxy Grand Duos .
Some ways include installing CWM but the CWM doesnt works in some cases , others include just rooting.
My recommended way is to first Install CWM and then ROOT it .
Using CWM (as a default recovery) its easy to install mods , roms and sripts .
A working way to do so is in the following post on Innotechive :
Visit Here For rooting and installing CWM(touch)