How do you use Arcance Echo

[Barca]

I have it. I was expecting it to give my next spell a duration of 20.
But all it seems to do allow me to cast a duplicate.
What spells do you use this with?
One with a long recharge time?
A 15 energy spell, Arcane Echo followed by another 15 energy spell that is worth something, then you have to wait to recharge to 15 energy so that you can cast 'the Arcana Echo' version?

[Feynt]

You use Arcane Echo (and Echo) with spells you either want to cast that have a long recharge time (like Energy Tap for some quick draining, but with such a long recharge you only get one cast) or short recharge spells multiple times (like Arcane Echo then Lightning Strike, a spell which recharges in 5 seconds). It's versitile, you just need to use it wisely. As a rule of thumb, don't use Arcane Echo with high cost spells unless you have the energy reserves to back it up (i.e. Elementalist prime).

[Tsume]

This is how you use Arcane Echo and what it does:

First you cast Arcane Echo, and then chose a spell to cast. Once you cast that spell, Arcane Echo emulates that spell for 20 seconds. Meaning that basically you give yourself 2 copies of one spell. And that is how you use it, and what it does.