I'm still a rookie Fire Warrior, but for me, I use a unit of three with Burst Cannons, no upgrades, and let fly. Under a hundred points, it takes up an Elite slot moving me closer to a bigger Detachment, and are just hard enough to be an annoyance while being just threatening enough to not be left behind. Parked in cover, you get a 6-wound unit that is -1 to-be hit, so you don't want to fire big guns, but who have a 2+ save, so they shrug off small guns, and a smaller unit doesn't worry about morale.
taking two, three, or more of these little groups can just wear someone out trying to deal with them and, if they don't, the high mobility of them allows you to snag objectives as well.
Just really, really darn handy.