The memory used by damage meters is static. Unless you don't have much ram, you'll not notice the gameplay difference. Resetting frequently will make login times faster, but it doesn't actually bog down your fps at all.
I guess there are no damage meters around matching oUF_P3lim or something. Maybe an author should make one? Anyway thanks for the tips, i'll check into Recount or ill stick to Violation. I guess it's not changeable?
Went there, actully messed around with all buttons/options for Omen, it didn't change it's interface, only the top bar where it says Omen3
However I found a "skin" option further down, where it says Blizzard or Omen (can't remember) but there was no alternative option to select, maybe I have to download some skin for Omen?
The options for the main Omen background/border are in the "Omen" root-of-the-tree options. You can add additional backgrounds by using the addon called SharedMedia (it comes with instructions on how to add your own media).