In general, Fate is a universal set of game mechanics, which can be easily adapted to use in any setting. EP Fate is going to be a sourcebook focusing on the adaptation of Fate mechanics to fit the EP setting. In other words, if you dislike the current game mechanics (rolling d100 for tests, rolling d10 for damage, character description using Aptitudes and Skills measured from 0 to 100 etc) and you would like to try something else, then the sourcebook will present you a way to do so. Fate uses its own version of six-sided dice and is pretty fast and non-obtrusive. In comparison, the original EP system is more oldschool and precise. For example, where Eclipse Phase uses many skills (Beam Weapons, Kinetic Weapons, Seeker Weapons etc.), Fate would use the 'Shoot' skill. Same with damage - where EP counts every single damage point and every single wound, stress point or trauma, Fate has a maximum of four 'Physical Stress' or 'Mental Stress' points. This is how the basic Fate system works, anyway; the conversion will probably add some new skills in order to reflect the specifics of the EP setting, but the number of skills will still probably be reduced greatly. Less number crunching, but also less precision. Some people simply don't like counting every hit point or every bullet in their gun. Some dislike long and precise character creation - they want to describe their character with a few basic aspects and be ready to go. Fate mechanic is for them. If you like the EP mechanic as-is, you don't need to buy the sourcebook. If you think that EP is a bit too rules-heavy for you, then you might want to give it a try. That's it, basically.