"Every so sorry to bother you but we are the borg, would you ever so kindly let us assimilate you? It wont hurt promise. Resistance is futile because if you say no we will just go away" So do you thing in the mirror universe the Borg would still be evil or would they be lovable friendly cyborgs?
Mirror Universe Borg Collective; where individuality is important, and they only assimilate you if you ask nicely.
Mirror universe Borg probably just give their own biological and technological stuff to others in the form of... giftwrapped cubes. I don't know.
I remember in one of the novels, the mirror universe Borg were even deadlier than prime universe Borg!
In the current Treklit continuity, the Borg of the mirror universe are pretty much the same, except for two things: 1) they have a King instead of a Queen, and 2) Their ships are diamond shaped.
The Borg in the mirror universe are fairly benign, as they only ever use their collectivity to caption pictures of sehlats and complain about the reboot of Captain Proton.
If I'm remembering correctly, there was only the one ship. And that was the King's flagship. Which would match with the Prime, where the Queen's flagship in Dark Frontier was a diamond.
Mirror Borg: You will be liberated. Resistance is futile. Your biological and technological individuality will be free from interference.
Mirror Universe Borg? Overall, nicest people you'd ever want to meet! A little snobby, though. They're constantly throwing people out of their collective.