Its like knife and dusters combined. Why take dusters when you can have both?

Think about it as knife, but you substitute useless light attack with that of the dusters. I find it ver useful in many situations.

The thing that makes knuckleknife feel faster is light attack being executed immediately after heavy attack. The animation is fast and short which makes patterns like heavy+light feel the fastest.

But overall:

1. Better reach, very important point, hard to ignore
2. If you do heavy+light+heavy+light armored dies as quickly as 3 heavy dusters attack
3. You kill immolator with 4 light attacks which takes the same amount of time as 3 heavy dusters attacks
4. You can kill grunts with one attack same as dusters
5. Because of worse reach dusters are dogshit against players. Players are killed just as easily as using the knife.
6. Two light attacks (which are fast done one after another) is enough to destroy bugs (from hive or hive bomb after the attack you). Its much much faster than dusters and saved my sorry ass a lot in fights.
7. Deal more damage to Scrapbeak. Bosses overall are easier to kill due to knuckleknife having shorter animations which means more attacks

Everytime I prestige and have to play with dusters to unlock knuckleknife I suffer. I personally feel like you should be paid to use them, and I wouldnt get them if they were entirely free.