The Cyclone is a fast avia unit specialized to provide support.
Very fast unit
High visual range
Good against infantry units and units that can't target avia units
Countered by any anti-vehicle units that shoot into the air
Vulnerable to other avia units except Dragonfly
Only moderate damage against vehicles
Cyclones are so fast they can outrun any threat except fighter jets, which makes them great for scouting enemy bases without many Anti-Air Towers or Porcupines while avoiding the opponent's army. They can also be placed on top of hills to be undetectable by scouts (except by other aviation units).
Besides scouting, they can be used to counter armies solely made up of Infantry units, to which Cyclones are a direct counter. This is especially the case against Grenadiers as they can't shoot aerial targets unlike their confederation counterpart, the Heavy Assault which should absolutely be avoided when fighting with Cyclones.
It's not a good idea to send them to fight against Armadillos or Porcupines, as both of them are able to win in a fight against equal numbers.
Cyclones are also capable of detecting both infantry hidden in forests, Barracudas submerged underwater as well as units hidden in the Chameleon's fog. This makes them a great option for removing spies from your base or enabling other units to directly target enemies otherwise hidden. This is especially useful when using units like Vertex, which are unable to force fire on a specific location on the ground.
Cyclone is also one of the few exceptions amongst units (the other one being Fortress and Hammer), where the tier 1 unit can tank more damage than its tier 2 counterpart (Vertex), allowing it to tank anti-air attacks for them (Cyclones Tank for Vertex).
With the introduction of Heroes, Cyclone received the ability to strafe, making its movement identical to Wasp, allowing it to move and shoot in different directions at the same time. Combined with its mobility that surpasses any and all ground units and its high range it can then kite lower ranged units like Armadillo (which previously countered Cyclones) and Heavy Assault, turning the battle far more favorable for it.
At higher ranks it can not only take on Caimans, Coyotes and infantry but also chase down and kill the tier 1 hero Wasp, allowing Assaults and Deltas to gather containers unobstructed.
Cyclones are also well known for their synergy with Seraphim in air mode. As both unit's movement type and speed are identical. At the same time, Seraphim is able to provide damage against heavily armored targets, something which Cyclone on its own lacks. In turn the Cyclones can draw the attention of anti-air to it to make it survive longer.