What does Rune Master medal actually do?
 

It says Rune usage bonus +10% but what does that actually mean?

The requirement is unclear too : "rune most often used in the first ten rounds of combat".

If somebody can clarify this please do so.

The requirement is to use up runes in combat. That's it. Very easy.

The effect, I'm assuming, is to increase the effect of runes in combat. I have no idea, however, if the +10% means Attack Runes now give +30% or +22% instead of the normal 20%.

I'm guessing on the effect, though.