UEF and Seraphim T2 Fighter/Bombers are very generous units by a long shot. You get what you pay for with interceptors, air-superiority fighters, attack bombers, gunships, strategic bombers and other forms of air, but it is important to stress that you get more than what you pay for with UEF and Seraphim T2 Fighter/Bomber units. A single fighter/bomber can do what four interceptors can do, and what four T1 attack bombers can do for less expense, especially in energy consumption. They are equipped with radar as well, and have a slightly better gun range and line of sight than interceptors. When it comes to airspace defense, the performance difference from Tech 1 to Tech 2 is hard to miss. Once you get your first Tech 2 air factory, switch production to fighter/bombers immeadiately.
UEF and Seraphim Fighter/Bomber units can also find usage in tech 3. When used correctly, they can take on air-superiority fighters and easily rival strategic bombers, which have an insane energy cost.
UEF and Seraphim Fighter/Bomber units are the perfect counter for Aeon Combat Fighters. As the Combat Fighter lacks a ground weapon, this is an unfortunate characteristic of the Aeon.
Some think that a Cybran T2 Corsair is not efficient against other air units. Because it has a third less DPS of other fighter/bomber units, they say it cannot do what UEF and Seraphim fighter/bombers can do when it comes to fighting capabilities. They think that this makes Tech 3 air-superiority fighters more important for the Cybran. However, the Corsair uses a homing missile weapon against air units, giving it an extremely high hit rate compared to its T2 counterparts; this accuracy makes its effective DPS much closer to the other two in air-to-air combat (as the weapons of the other two can and do miss). This homing ability is lost when targeting ground units; however their ground projectiles all hit one spot and travel extremely fast, giving them much higher ground accuracy while having the same ground DPS. They are very good at sniping for this reason.
The UEF Janus is basically what happens when you take a Cyclone and a Scorcher, make them better, and then put them together. Its has, not surprisingly, the highest HP of the other two fighter/bomber units. Rather than dropping one bomb, it drops several ones in two rows, making it perfect for damage over a wide area, but not highly effective against units with higher health, like an ACU. With damage over time, units that are out of range of the bomb can accidentally move into range and get damaged themselves. Therefore, the Janus is probably the best unit for taking on groups of T1/T2 units. The Janus also is able to defeat Aeon Swift Winds 1 on 1 due to higher hp and equal DPS.
The Seraphim Notha releases all its damage output in one bomb, rather than having it spread over several bombs. This makes it the best fighter/bomber for sniping/attacking stationary targets, like Mass Extractors or T2 power plants.
If you are able to build these, you are able to build Air Staging Facilities. They cost substantially less than any fighter/bomber.
Because of radar capabilities, attack capabilities and a better fuel supply, fighter/bomber units are much better for patrolling your base, and should replace most if not all of your defensive interceptors and attack bombers ASAP.
Fight/Bombers make good use of Tech 2 base defence, as many groups of a Fighter/Bomber with two intercepter escorts make very good patrols during Tech 2 and can even fair well into Tech 3.
As aforementioned, some think that Corsairs are not well suited for taking on other fighter units. As also aforementioned, the Corsair's accuracy (with homing missiles) makes its effective DPS much closer to its counterparts and others think it is a perfectly competent unit for taking on other fighter units. The weaknesses of T2 fighter/bombers that most can agree on can be found below.
Concerning fighter/bomber units in general, their fuel supply, while greater than the fuel supply of Tech 1 air units, is not great enough to justify long-term usage away from air-staging facilities. They lack the speed of combat fighters and other higher tech units, making them ill-suited for chasing down anything but Tech 1/Tech 2 units, but they don't suffer from the illness of being too fast as ASFs sometimes do. Thus, they should still be kept around in numbers as secondary defense units, mostly to hit the stragglers that your ASFs didn't get (usually gunships and trasports) or any land units that are out of point defense range. When used this way, you can bring your ASFs much less damage and overall bringing down the cost on your economy.
Like most Tech 1 and 2 air units, It is highly recommended to avoid flying over T2 AA Flak defenses. However, Fighter/Bombers (Especially the UEF Janus) display a remarkable resistance to T2 Mobile Flak.
The UEF Janus is likely named after the Roman god of choices, beginnings, endings, and doors and is usually depicted with two connected heads facing opposite directions. It is probably named as such due to the fighter/bomber possessing two "faces" with its dual role.
The Janus has a variable-geometry wing, meaning that it changes shape in flight. In normal flying, the wings extend out normally. When engaged with enemy aircraft at close range, the wings sweep forward, giving the aircraft a trident-like appearence. This would most likely be a feature to increase the aircraft's ability to turn harder at speeds, as it gives less drag.
The Janus does not appear in the unit list that comes with Supreme Commander for the PC.