Black Spindle is CRITICAL for Warpriest/Golgoroth. Touch of Malice is CRITICAL for Sisters/Oryx. Both guns are close to useless for all other parts of Destiny. However, even with such limited use... both guns are among my most prized Destiny possessions. ;)

I can't speak for Touch of Malice. I never leveled it (thus never really used it) since I'm not farming those fucking Hadium flakes.

Last night I tried my newly acquired Touch of Malice on the Oryx fight. I didn't love it. Maybe because it's at 310, maybe I just need to get use to it? I dunno.

A 320 ToM can take down ogres by itself almost fast enough to complete the Oryx challenge (it's non-trivial, because you have no margin of error, and others will have to get the 4th knight... I don't know of any other weapon (or weapon combo) that can do that consistently. This is only relevant when you're down to 5 players, but that happens occasionally, and not having to wipe is a nice thing.

I generally find the Oryx fight goes more smoothly if you have a couple ToMs in the mix, but not too many. They're great for killing Ogres, and critical for keeping Oryx's chest open during the bomb detonation, but they're not so good for dealing with general mobs. We did really well last night having a mix of ToM, Black Spindles, and Sleeper Simulants all going at the same time. Our snipers were taking down Ogres in the blink of an eye (I often barely had time to fire a 2nd shot at them), Sleepers were blasting Light-Eater Knights the moment they appeared, and ToMs kept Oryx vulnerable while the rest of us detonated the bombs. We finished 3 Heroic Challenge battles in 3 hours, which is pretty smooth all things considered :)