Excerpt from "'Should I Buy It?' – The Last Word & Other Exotics"
Starfire Protocol is one of four Warlock chests. The other Sunsinger chests are Voidfang Vestments. Aside from the Fusion/Heavy ammo benefits, Starfire grants you a second Fusion Grenade.
NOTE: This Exotic does not stack with the class talent Gift of the Sun (additional grenade).
It's good gear for someone without Raid boots (Heavy Ammo) and/or likes the talents Touch of Flame or Angel of Light. Starfire Protocol basically just lets you spend your far-right talent on something other than Gift of the Sun – but even then, you're now limited to Fusion grenades. The extra Fusion grenade is nice, but a second grenade takes twice as long to regenerate. (At max Discipline, that's about 1 minute.) Since it doesn't stack with Gift of the Sun, it's not a complete game changer like we'd hope. Our favorite thing about Starfire Protocol is the hefty Intellect stat, if that says anything.
Ultimately, it's an okay Exotic only worth it if you main Sunsinger. Otherwise, wait for Heart of the Praxic Fire.
TIP: Can't get enough grenades? Try this odd PVP combo: Gift of the Sun + Voidfang Vestments. Two grenades on-spawn!