Just like the Killflash, the scope extender helps to mitigate reflections of the scope lens that can give a away your position.
Combination of these makes it impossible to get any reflections at all. In addition to this, both of them protect the scope body itself from accidental damage and bb impacts.
The Scope Extender Mk1 fits on Sniper Scope Set Mk1.
The Scope Extender Mk2 fits on Sniper Scope Mk2.
Be Effective
It's slim construction doesn't add much weight to your scope setup. Killflash and lens caps can still be used with the scope extender.
Looks
Besides all of the benefits described above the scope extender also adds a lot to the overall aesthetics of your rifle setup. It's just makes your rifle look much cooler in my opinion.