Vertexes are by far the most versatile unit in the arsenal of Confederation which can be used for reconnaissance, frontal assaults and defense.
Extremely fast
Very high damage
Very good cost efficiency after the Avia Factory and Airfield are already built
Needs to refuel, causing it to have phases when it is completely vulnerable
Can't attack units which are hidden away without additional support units
Can be sniped indirectly by attacking its airfield
Vertexes are available beginning from HQ3, and aside from their production building, also requires an Airfield which supports a maximum of 4 aircraft each.
Vertex have the highest visual range and movement speed in the entire game, which makes it possible to let it scout a base from the outside, without truly entering it and exposing the Vertex to enemy Anti-Air Towers. This means that it can often be reused for further scouting or other purposes after completing its tasks. It is recommended to only let 1 Vertex fly around the enemy base for scouting to avoid losing multiple.
Unlike the Cyclone, Vertex can't detect hidden units like infantry in the forest, but it can attack them when another unit reveals them (with the exception of Barracuda which needs to surface to be attacked by Vertex).
Vertex is a great unit for sniping units or buildings which are not defended by Anti-Air Towers or Porcupines as it deals enormous damage with each pass. A good trick to make it a lot stronger is to order it to turn around directly before shooting at the target and, with the right timing, will allow them to still shoot at their target while avoiding the enemy's anti-air attacks, therefore greatly reducing the damage taken by it. It needs to be noted though that this tactic needs practice to be pulled off successfully, because if the timing is to late, it will fly over the enemy base and take a lot of damage and if it is too soon, the vertex will not shoot at the target at all.
Another more difficult trick allows you to almost double the fire rate of the Vertex, by letting it fly in a circle and letting it attack enemies on two opposite sides of the circle in quick succession. Using this tactic needs to be thought over very well though, as it is very micro-management intensive and can leave your jets very vulnerable to anti-air attacks.
Furthermore it is possible to send in a Thor a few seconds earlier to soak up anti-air missiles, therefore allowing Vertex to harm targets in the middle of strong air-defense without taking any damage.
Due to their extremely high speed, Vertexes are able to catch all units in the game, allowing them to punish air raids on your base extremely well, by hunting and destroying retreating/attacking Hawks and Albatrosses. Experienced players can go so far with this type of anti-air defense, that they don't even need to build any additional Air Defense.
They are also very useful for supporting Naval Platforms defending against navy by either sniping the enemy support avia or directly targeting enemy ships. This is especially important when Barracudas are used to attack, as they need to surface to be able to outrange Torpedo Platforms, therefore leaving them defenseless against avia, as they have no built-in anti-air weaponry.
Last but not least it needs to be said, that it is advisable to start using Vertex as soon as possible, as learning to use them is that much more difficult at high ranks, due to Vertex gaining a lot of additional speed and maneuverability through upgrades, leaving even less time to properly react when controlling them.
Vertex also has a massive attack range, allowing them to pick off Alligators and Poseidon that are out of their formation or at the edge of it. But they should never attack the formation directly. Instead, it makes sense to kill 1 or 2 navy units without loosing any Vertex and then let them recover their health on an Airfield before using them again.
A good rule of thumb when using them is the resource rule: Only attack if the gains outweigh the losses. Vertex is the fastest unit in the game, so it is always possible to decide whether to engage or not to engage.