OP already already marked this thread as answered but anyway...

After putting more than 1000 hours into this game, getting every single achievement and more importantly using both Vanilla AND Invictus I still feel that I would be really arrogant if I commanded OP what to do since he was just asking for opinions, not commands. If I had not ever played Vanilla OR Invictus I would not even consider writing my opinion since I would be lecking 50% of knowledge to provide an opinion based on those two, similar but different, experiences.

My opinion is that Invictus is a venilla friendly mod and it adds more to the game than it may detract. BUT my humble advice -not command- is using both Vanilla AND Invictus so you can develop your own opinion on the matter.

And about mods, eveyone is free to use them or not. Far from me to pontificate about always using mods or never using mods.
We have mods for bigger boobs. Or to include coussin´s Rory face in the game.

And we have mods like Invictus that fixed many bugs and was partially adopted in the augustus patch by Paradox as they acknowledge in the patch´s description. Or mods that make a 2010 game like New Vegas playable today, get rid of thousands of bugs and restore original content.
Any person who stops a moment and consider the issue will understand a simple truth: in mods, like everything else in life we have quality work and lousy work. I tend to play without mods bur for some exceptions like Imperator BUT even so I can see many modders put hundreds of hours and love into their work for no reward. Respect.

One last consideration, in the augustus patch description it was said that it was necessary to divert resources from Tinto team in Paradox to make the patch happen. Since the are no teams working in imperator -that we know of- it seems safe to assume there is no chance to integrate anything in the game, mod or no mod.