These are to be used almost exactly the same as Guardian Defenders. These are some of the best troops you can buy, in the Eldar army. These guys are excellent at taking out 2 things. First, they are good against large creatures who rely on a high toughness, such as the Bloodthirster or Hive Tyrant. Next, they are good against fast moving squads with light armour, such as Hormagaunts.
Sniper rifles cause squads to test for pinning, if a wound is taken.
This can help slow down squads like the Hormagaunts, giving your Guardians time to shoot them to pieces with shuriken fire. I've had a lot of success with this tactic. These used to be some of the best soldiers in the Eldar army, but with the new rules, they are nothing too special. They move fast, as if they had jump packs. Their weapons are good at strength 6, but lack an AP value.