I saved 6000certs for the new lib update, bought the weapons and can't find any loadout that works effectively for the Duster. I have everything Maxed out. Any suggestions? (besides don't use it).
Try running with stealth to full and a non-faction-colored camo. That will allow to hover 10 feet above the enemies without looking suspicious, which should be close enough to fire a few accurate shots before they figure out what's actually happening. Then either use afterburners to get away quick, or have fire suppression to fix the damage the enemies will definitely cause when they look through your clever disguise. If you enjoy less extravagant methods, just grab a Zepher and stay within 180 meters of the enemies, or whatever the range of Thermal is.
There isn't one. It's a highly inaccurate weapon without the splash to make up for it. It really doesn't have a role, since the Zephyr is simply superior.