Great secondary capacities, and with the advent of long range anti-bomber missiles, they're my friend. 
I admire them, but they'll be the death of you in a dogfight, which is where most of my missions end up. They're okay if there isn't more than one-two shivans on your six. When you tend to charge into shivan formations pretty much rubber-banding the trigger only to fight your way out of eight maras sinking their teeth into your ass, the Ares isn't for you.
Against bombers though, that's when they really shine.
EDIT: The AI doesn't seem to use Trebs very often when I observe them in the closing missions of the retail campaign.
