Not at all useful for your sader, unless your gears are crap to begin with (even then, usable but not useful) - for knight class, it's okay. It does good damage in prison and high orcs, but it is somewhat limited due to being unslotted and 2h. Still, if you train in those places a lot it's a decent spear.
However, I liked hellfire better for niff. Unlike brionac, hellfire can actually hurt disguises, so if you want to niff you'll want hellfire (brionac is a pain for killing disguises). Aside from nib, I consider hellfire the best niff weapon for the knight class. On the other hand, without decent gears (eddgas, deviling) you won't be able to niff until higher levels (80+) anyways, and until then brionac will be more useful to you.
Since your budget seems low, I'd recommend you do get the brionac, just bear in mind you might want to or have to sell it again later and get something better.
