General

I think of it as an easier opportunity to get an item to legendary or just get good potential

[quote=Johnny2by4]Does this mean that we use the cube twice or you get double the chances?[/quote]

You get double the chance of it working.

BUT- that means if the normal chance of raising the tier is .01 (one out of 100)
Then "Double Miracle Time" means the chance of raising the tier will be .02 (one out of fifty).
Still not very good chances.
* (I have no idea what the actual chances of cubes working is, Nexon won't tell us. This is just an example of what "double" means.) *

Is it worth it..?
You decide.

[quote=Gomrathz]makes me wonder if the ratio of increasing ranks still makes it 2x more easy to cube items from unique to legend. because it will be only 1 rank instead of double[/quote]

Nah there's probably some messed up formula there to screw over people from cubing from Unique to Legendary.
Source: Myself

makes me wonder if the ratio of increasing ranks still makes it 2x more easy to cube items from unique to legend. because it will be only 1 rank instead of double

I hate cubing.. @___@

If you cube regularly, and you have some good equips, I would say it's worth cubing.

I wouldn't know for sure though, I don't usually buy cubes with NX

It's worth if you have alot of Rare stuff not Epic

Oh wow. Thank you. Do you believe its worth buying?

There's a chance to raise equipment potential rank twice in one cube

So you use a cube on your equipment, let's say it's a RARE potential. If you do get lucky, the potential raises twice. In this case, it goes from RARE to EPIC to UNIQUE, well it actually skips EPIC but you get the idea.