I can't open your photo (Facebook's blocked here), but I will tell you right now that the Ben Nye stuff is a PAIN IN THE KEESTER, especially if you're shooting for uniform coverage. It goes on a bit streaky in my experience (fine when you're doing grey, not so good when you're trying to do, say, a lock of white), is a mess and a half, and leaves your hair feeling like it was glued together. Once it dries, it will come off if rubbed or gotten wet, but stay on relatively well if there's no contact.
As Shadow Warrior says, a wig would be better. However, I'd say that one ounce of the stuff would definitely work for covering a minimal beard and whatever flyaways escape from under the wig.
Therese von Ludowing (Sound Horizon's Märchen)Elsewhere: Tumblr ~ ACP ~ CosplayLab
Catelyn Stark (A Song of Ice and Fire / Game of Thrones)
Elisabeth - red ballgown (Elisabeth - Takarazuka version)
Thessaly (Sandman - The Kindly Ones)