Since I own a maskeraith I can tell you that these quills are quite an interesting additional damage output with even more additional poision damage, but it would be more useful to one enemy instead of a group of enemies.

However, a quilled enemy plus a fire phiol can kill a gun puppie or a Jelly Turret -> quill a Jelly Turret, throw a fire phiol and see it slowly struggling to death while you hide yourselfe out of its range, mwahaha! (Since now I did only use a Neutral Harnish. A Shadow one might be able to kill it with quills only, but I can't confirm that.)

(Additional note: your pepperpox should deal the necessary fire, too, so you won't need a phiol)

Upside of Quills:
-Poisions with strong poision a group of enemies and makes other weapons deal more damage
-You can literally snipe out one enemy you don't want to fight for long

Downside of Quills:
-You need to deliver enough hits before quills disappear to use its full potential. I can't recommend using a slow weapon.
-You can't spamm all enemies with quills because of its cooldown time. One ultimate version spreads quills pretty good, but it is no exchange for a secound weapon if you face many monsters of a type that your main weapon is resistance to.