Yep - its a tough one, in actual fact the Termis are not the best made cans, but they are the "right" cans for a Duacti. I'm not sure of the build quality of the Microns, but many of the Termis do fall short of the production qualities of other exhaust manufacturers.
If its the right name you're after, go for Termis (or termi stickers,
.
But sticking with Microns will offer no power advantage or disadvantage (unless you go for a larger system) over the Termis.
I assume your pipes would be a 45mm end can system, a swap to 50mm end cans is an option, some power could be gained, but it would probably be minimal unless it was in conjunction with other mods. You could go for a full 50mm system, but again minimal gains - it would sound great though.#
One more thing - do you know if she has had the chip swapped to support the Microns? Might be worth checking to ensure that the fueling hasd been modded to suit the open cans.
Tim