Jeff, are you sure it doesn't have any curing salt in it already? Many dry jerky seasonings have #2 Prague powder in them, for use as a rubbed cure (where you don't mix it with water). This one seems to maybe actually be a brine, since it says to add water? Curious...going to have to investigate!
I just looked it up, and see that it is, indeed, just a seasoning mix! States "does not include the sodium nitrite cure." If you put it in a liquid brine, you should add #1 Instacure (Prague powder, 6.25% nitrite). If you intend to rub on the meat, place in a plastic bag, use #2 Instacure (nitrite and nitrate). The idea of using #2 for a rub is that the nitrates convert to nitrites, over the length of the cure. Brines need pure nitrites.
Bet it's a tasty blend!