About G Duel Infantry 3
If I give G Duel Infantry 3 to my +10 Nino, is she going to score 170 or 190 BST?
And, is that worth to do? Or it is a waste of orbs and Helbind?
She'll be treated as a 170 BST unit (the same as +Spd Sheena or +Spd Gwendolyn).
Only do it if you use or like to use Nino on your Arena team, if you just rather not waste as many Crests for score sniping, or if you are on the border to Tier 20 -> 20.5 or Tier 20.5 -> Tier 21 and really want the extra rewards. Just realize that she won't be able to kill anything if you want to get the maximum score.