The extended enhancement focus items extend all beneficial enhancements (buffs), including SoW.
If you have the equipment on, your spells will last 15% longer. Level 1 focuses are good for all spells level 20 and under, level 2 is good for 20-44, level 3 up to 60, and level 4 to 65.
I recommend the Lockjaw vest if you're under 24. Bat-fang after that.