What exactly is the point of suggesting a Gran Faust for JK if the entire point of running JK is to get the Sealed Sword to begin with?
Gran Faust
Well, the Faust is the only weapon in the game to inflict curse on its victims, that alone measures its worth. Plus i'm a bit more able with it than the Silent Nightblade, each to his own.
But seriously, have you ever cursed a Mender? Seeing that big purple eye above one makes me pull a Trollface every time it happens. Also with PvP due soon, Curse is pretty much a Good Game if your target isnt aware of his/her condition.
I'd suggest it, but more on Faust. Gran Faust is not really so necessary in a relative sense of reaching for a 5*, as DA's more worth that endeavor. Faust has the wide sweeping reach to attack multiple Jellies at a time, so that's convenient.
It's also because JK is very popular as not just a grind for the equips (there's also the [Divine] Avenger and Silversix/Argent Peacemaker to go for, not just Faust), but also because of the large amount of crowns and heat you can get, that you could get more of when the Faust helps you go through the runs faster.
tl;dr
Grinding tool makes you grind faster.
I'd never suggest the Faust line for Royal Jelly. Nightblade line for me all the way.