An opponent gets a warning when a missile is "locked on" - fire an avril above your opponent; and lock on (centre your crosshair on your target) when the missile is as close as possible. This gives your opponent no warning.
Against a more distant target that's fast moving; locking on intermittently (not using secondary fire) gives your opponent a false sense of security
You can have 2 avrils in the air at the same time.
Firing an avril away from a target that is firing at you, may prevent your own avril being blown up in your face.
If an opponent is on fire- finishing off with shock primary is usually simpler than firing another Avril.
Double damage and avrils will never cease to surprise your opponent who thinks he can absorb a single blast.