>>530085915
1. Recoilless requires a backpack, Quasar doesn't.
2. Quasar can still one-shot Hulks and Gunships, while also killing non-Annihilator Tanks with a single turret shot and killing Annihilators and Cannon Turrets with a good heatsink shot. Only thing it doesn't deal with well is Factory Striders.
3. Infinite ammo, meaning you can use it on any target of opportunity including cargo container doors.
4. Killing Fabricators at zero ammo cost is significantly more useful than you give it credit for, given how many Fabricators there are in any given mission.

As someone who regularly solo roams on bots, it's excellent for giving you the ability to kill heavies and spawners without requiring ammo or taking up the backpack slot. Not taking up the backpack slot lets you equip something that gets shit done like Portable Hellbomb, and infinite ammo means you're far less liable to have to call down a Resupply just to restock.