Before I begin, I'd like to say that I greatly enjoyed the "mirror universe" mini-arc in the Cardassian Front - the story was good, the battles were fun, etc.
That said, I'd like to propose a couple of adjustments to these missions and to the Terran Empire faction in general:
1 - I noticed that the faction is almost always referred to as the "Terran Federation" rather than the canon "Terran Empire", with no in-universe explanation given or even hinted at. While this isn't a big deal, I think that either an explanation should come in at one point in the missions (perhaps when conversing with James O'Brien?) or it be exclusively called the Terran Empire.
2 - I like the purple hull material on the Terran ships, but they look a lot like the material on Jem'Hadar ships. That's not really a problem, but it makes the Empire a bit less...distinctive, in my opinion. Perhaps a pale red color would be better? I know that's a matter of personal preference, of course, and it's not really a big deal anyway. Just something to consider.
3 - My only serious nitpick: there appears to be a glitch in the "ship name" system - in "Crack in the Mirror", the three runabouts are all called I.S.S. Runabout, the transports are all I.S.S. Transport, and the three frigates near the end are all I.S.S. Ship. In "The Other Side", the three battleships in drydock are all I.S.S. Battleship, and the three drydocks are labelled on the mini-map as I.S.S. Drydock. A fix to this would be much appreciated, for the sake of immersion.
4 - All Terran Empire ships and assets should be useable in the Foundry. It's kind of unfair that all the other factions have mostly everything, but the Terrans - apparently a popular faction in the Foundry - have nothing but two mislabeled ships ("Federation Battleship" and "Fek'Ihri Dreadnought").
5 - The fighters should be called "Terran Raider" (their canon designation).
I hope I don't come off as whiney or demanding. I like the missions, and most of STO's missions are lots of fun. The above are just things I personally would like to see addressed in some way, whether in a patch, a remastering, or a future mission.