Extremely useful in both PVE and PVP. It's damage is like a bad burst-SideArm. It's slower projectile speed, less damage and fires less often... But it is free nonetheless and the projectiles track a bit. Even a bad SideArm is good, if it is being shot for free while you shoot your normal weapons. Final boss, has a nice damage phase to use it on. Even better when it's from the empowering rift in this phase. PvP, with a co-ordinated team that knows when your rifts are down... it is godlike. Get flanked by their sword dude? It's okay, 4 peoples Arc Sols will rip him apart. TL;DR It's an incredibly useful talent across PvE and PvP especially in end game content, due to end game content requiring co-ordination and optimal Arc Sol useage is via having all fireteam members stand in it, often requires telling them to.