Not much to expand on beyond the title. The trait Final Salvo should be applying stability to the Scrapper and each gyro as they are summoned. This works for all gyros except the profession mechanic Function Gyro.
I have tested this in PvP only, both in matches and against the profession NPCs. I have never gotten stability from using Function Gyro with Final Salvo equipped. All other gyros give stability as expected.
[TNO] Gizmo Gigawatt (Engineer)
Jade Quarry