Afterburners provide a speed boost from 105% to 171%. Afterburners fit into a Mid-slot and scale with the ship classes: 1MN for Frigate-class, 10MN for Cruiser-class and 100MN for Battleship-class ships. Compared with Afterburner skill.
Changes due to the Apocrypha patch have allowed both Microwarpdrives and Afterburners to be used in complexes (previously only Afterburners were allowed).
Tech 1, Named, Faction, Deadspace, Officer
Steady capacitor consumption as it cycles
Longer ship alignment speeds whilst it is active (though using for only 1 cycle will actually decrease alignment in all ships with natural or modified aligns greater than the cycle)
Afterburners don't provide anywhere near as much of a speed boost as a Microwarpdrive, roughly 100-125% boost rather than 500-625% depending on skills (some modules have a greater innate bonus) but come with less penalties.
They add mass to your ship. This is not really noticeable unless you try to fit a bigger afterburner than normal for your ship class, at which point your inertial increase will make your orbits very large (this is to prevent small ships from avoiding MWD penalities while still getting similar speed boosts from bigger drives combined with the tight orbits they normally enjoy)
Advantages vs. a Microwarpdrive
Considerably less skill and fitting requirements
They can still be used in Mission deadspaces that interfere with warp fields (this is not a big issue anymore, as almost all deadspace areas now allow MWDs)
They don't have a penalty to Capacitor size (and thus also GJ/s), and don't use nearly as much capacitor per cycle (higher afterburner skills can allow cap-stable afterburner fits, which are much harder to achieve with MWDs)
They don't have a penalty to ship signature radius whilst active.
Warp scramblers will not shut them down as they would a MWD.