Small review because I may as well share my experiences on it
Instead of writing a whole analysis, I'll just go through the feature list and comment on it. I know this will be unpopular among the hype, but I'm still going to say it-
It's not that good
It's a shame they come too late to be of any real use in single player, by the time you get to unlock these through researching several rare technologies(So it's possible you won't ever get to anyway even if you made it your goal for the game) you'll be able to steamroll the galaxy with minimal effort.
They're shiny, but aside from the sensor array they don't actually do anything that you could actually reliably want at that stage of the game without being able to already get it elsewhere.
Actually works somewhat decently, though with how more planets increases the cost of research and the unity needed for the civ 5 tradition copy. You may want to make a few because they're roughly equal to a decently managed planet per tile, but since they are small and have some very strong drawbacks they will never be amazing. You will not 'go tall' with these as the feature blurb says, If you're in a confined empire you won't have the resources for them. And if you're not confined, you're going to still want them anyway because they're decent to have. They're just something everyone is going to end up getting. Costs one of the ascension perks, but it's not like those perk slots have any serious competition going for them.
This is the main thing for this DLC and it's actually pretty good. The sad thing is that there is a clear "Good" and "Awful" collection of perks for this that makes it clear that you will likely pick the exact same thing every game with the exception of the actual ascension path. You're going to just get the same things because the alternatives are just not useful.
Curious to see this listed as a feature, since it's just a single button for something that is a very minor part of the game. You can take a planet with people who don't have space tech and indoctrinate them into your ethics.
I'm having trouble figuring out any point at which this may matter, so I'll just move on.
In this paid DLC, we get tools for things that really should be in the base game. I'd like to ask Paradox for other useful DLC next, perhaps a management window for a planet's build-queue, a functional military that isn't just throwing everything at the enemy stack, different FTL methods that aren't just limiting yourself for the sake of it, or making it so slavery is actually useful for something other than encouraging rebellion on your own planets.
Support for the things people were doing already, now with small bonuses and made official. Most of it is of questionable use, but there is no denying that hive minds are pretty nice to have and a few of the things are nice and flavourful.
In the end, is it worth 20€?
I highly doubt it. You're going to have to get it eventually because it's essentially content missing from the base game and some small flavour things. But when you do, make sure it's on sale