Masterwork rune

Can anyone help me understand how this works exactly? I cannot find any info about it and i do not want to mess my runes somehow. And i dont know how strong is the upgrade either pls help

It upgrade Greater "X" Rune into Perfect "X" Rune. I also find it odd that you need to use it on a rune that is already socketed but that how it works. Also, Perfect have the same effect as Greater but with bigger number (not like the Essence for example).

thank you!