The OEM swingarm is short and beefy, made from thick aluminum which is light.
The extended swingarm in the picture you posted is long and skinny, but made of steel for extra strenght.
OFC aluminum is lighter than steel but that aftermarket swingarm looks pretty skinny so it won't weight much more that an OEM swingarm.
The only advantage of an extended swingarm is extra stability a wheelie prevention on hard accelleration which is good for drag racing and roll racing. A much longer than stock bike handles worse when cornering compared to original.

 

The OEM swingarm is short and beefy, made from thick aluminum which is light.
The extended swingarm in the picture you posted is long and skinny, but made of steel for extra strenght.
OFC aluminum is lighter than steel but that aftermarket swingarm looks pretty skinny so it won't weight much more that an OEM swingarm.
The only advantage of an extended swingarm is extra stability a wheelie prevention on hard accelleration which is good for drag racing and roll racing. A much longer than stock bike handles worse when cornering compared to original.

Thanks for your attention.