For 5 points and a grenade slot this upgrade adds a new weapon to the unit with one red die and adds surge to crit to the unit as long as one grenade is in the attack pool.
Frag Grenades are a halfway point between Impact Grenades and Concussion Grenades. They aren’t exceptional against armor or units in cover, but are not bad against either. In addition, if the target is unarmored and in the open then Frag Grenades are better than the other two giving all three grenades their own specialization.
This is a very useful upgrade for units that want to get close to their target and either need to be able to deal with Armor or cover, or increase their damage output at short range (if they normally roll less than one red die or don’t surge). While Impact and Concussion Grenades tend to be better on Imperial troops over rebel troops, Frag Grenades are better on Rebel troopers than Imperial troopers as they as they add surge conversion on attack, but it is not recommended on Fleet Troopers as their 2 white dice is on average pretty close to 1 red die and they already convert surges on attack. Because grenades add a new weapon for 5 points, the more figures in the unit that can use the weapon, the more efficient the upgrade is.
Imperial Royal Guard Expansion, Wookiee Warrior Expansion,