Excerpt from "'Should I Buy It?' - Dragon's Breath & Other Exotics"
Sunbreakers are one of two Warlock gauntlets, and the only pair specific to Sunsingers. The other Sunsinger Exotics are Starfire Protocol (both Chests). Sunbreakers extend the duration of Solar Grenades (from ~3.5 to 5s), especially noticeable in Radiance when multiple grenades litter the map. Faster Special Weapon reload is very useful, and Serpent's Tail is decent for PVE.
They're not the absolute best choice for Sunsingers, but they're worth owning for Sunsinger mains. You'll come to appreciate the quick Special Weapon reload speed. The extended Solar Grenade duration isn't much, but it's enough to say "Stay the hell out, this room is mine for a while."
Like Dragon's Breath, Solar Grenades are all about denying & forcing movement. A well-placed Solar Grenade can disperse a contested Control point. They're also good for low-mobility mobs in PVE and crowds of enemies (e.g., Phase 1 of Crota's End).
(Can't get enough grenades? Try Gift of the Sun (perk) + Voidfang Vestments. Two grenades on-spawn!)