FASA Games, Inc.

the spell effect test can be used only 1 time in the duration right ?
so the user can decide if using it as an attack step or a damage test, but once he uses it, is gone
i am right ?

I see how you get there, but it's not supposed to be that way to my knowledge. Rather, you can use it for one of the tests the whole time, but not both.

ah so you have the choice to decide wich to use (and i suppose you can change all rounds) but still you have it for the whole duration ?
zomg is a very powerful spell so

Well at least for Melee Weapons, you'd get +8 above your typical fighter if you're using Willforce. You wouldn't benefit from any Rank Bonuses from thread magic, though. And you couldn't use it for extra attacks because it specifies Melee Weapons. If you use it for Damage Tests, you couldn't use many of the damage enhancing talents. In essence, the Effect Step replaces what you usually do, and so you only get straight test bonuses ("+1 to Damage Tests" and the like).
At the same time, you're probably giving some of your buddies a darkness penalty.
That one's a bit odd, though, because it automatically happens. It's very situational.