About blessing from March of the Legion

https://pathofexile.gamepedia.com/March_of_the_Legion

So the blessing effect currently work like this:

It turn the supported aura (Wrath in this case) into an active skill
When used your character will:
1. Perform cast animation for 0.5 second
2. Spend 50% of your mana and gain the aura effect that last 11.4 second
3. After a 0.2 second delay, reserve 50% mana for 0.2 second

I found this item very interesting but the mechanic is kind of weird and unsatisfying to use. It already took 50% mana to cast, why do I have to reserve 50% mana after casting? It basically means you have to pay the mana cost twice to cast the spell once, which is very weird. And why is there a 0.2 second delay before the reserve is applied?

The effect will be a lot more better if either the delay or the reserve mana part is removed.