To state as directly as possible...
1: Increase Spell Duration by 15%
This means that it affects the spell at the time it is cast. By 15%. This stacks with AAs only.
3: Limit: Spell Type(Beneficial only)
As in doesnt affect DoTs, Taps, Recourses, etc.
6: Limit: Min Duration(24.00 sec)
As in will not affect spells like Yaulp. Sorry clerics.
7: Limit: Effect(Reaction Radius excluded)
Wont affect spells like Calm or Harmony.
8: Limit: Combat Skills Not Allowed
Duh? These arent spells anyways.
This is a focus effect
As in NOT A SPELL, and it CAN NOT BE CAST...
These items can be extremely useful however. an extra 4 minutes of SoW, an extra 2 mins of DS... an extra 15 minutes of riftwinds... yeah, useful :)