last time i thought why not try one of those (I picked a Anti-Borg one for Space STF's) and see if it helps the damage output.
I tested the Doff in Kerrat, but after a few engagements with probes watching the weapons tray i did not see any improvement in damage output. Though i was still in Red Alert condition, the damage was still the same as without the Doff slotted. I compared the damage numbers with weapon energy at 125.
After playing a couple STF's i am still not sure if it works, 10% more or less is not easy to tell from feeling.
Did anyone take a closer look on that and found out how and if it works?
They don't directly affect your weapon tooltips, but if you parse the combat log, you'll see that it does indeed improve your damage against the relevant enemy type. The problem is Cryptic math (TM). The bonus is applied to your base weapon damage at 50 weapon power and does not scale up. So although it may claim to improve your damage by 10% it will, in practice, only really affect it by ~2.2%. This is pretty much how all the math in the game works and is incredibly misleading, but they don't really seem to care, so get used to it.