These are fantastic for Ballista, people like to do hit and run attacks on Rangers and lightly armored PT members and this will stop them in their tracks or halt their escape so your DD's can move in and gang-smash them :P
If you're a ranger in Ballista i'd suggest bringing a stack of these.
The additional effect also procs on Weapon Skills if you have the ammo equipped, Slug Shot with an additional effect of Stun... yum!