Chuunibyou demo Koi ga Shitai! Movie: Take On Me Mini-Drama - Koukai Chokuzen no... Kaiko Gekijou

Take a look at the discussions: you can find a link to a YouTube playlist with all the 24 episodes there, with English translations.

Indeed, it is not important at all, just some fun little 30 second long shorts with some summaries of previous events and character presentations. The shorts all relate some bits of information about events and concepts of both Season 1 and Ren, such as the name of the circle (society), Yuuta and Shinka's past as the Dark Flame Master and Mori Summer, the Vanishment This World and Physical Linkage chants, etcetera. You won't miss out on absolutely anything new here.

However, there are ... also no real drawbacks. It's around 8 minutes total for the whole 24 episodes, and with the English translation in the discussions, you can comfortably sit down to reminisce about the cast's antics for a little while. if you're extremely into Chunibyo just like me, then I'm sure you'll enjoy 8 minutes of cute chibi dialogues between the main cast.

TL;DR: 8 minutes of extra cuteness, not necessary at all but also very easy to watch.

Even if you are a completionist like me, you shouldn't worry about this one.

These are all 20 second clips uploaded to Twitter. There are no voices, 2-3 generic music tracks that are probably from the regular OST and just paint animation with moving mouths and speech bubbles. I'm not even sure why I watched all of these, since I don't speak Japanese anyway. If you can read the language, there might be a bit more enjoyment to be found here, but this is very simple promotional material and you are not missing out on a super secret Chuunibyou special by skipping it.