Before you read the K-On! Highschool it is highly recommended that you either read the original K-ON manga or the first two seasons of the anime.

The general tone of K-ON Highschool is very similar to its prequel: a light-hearted slice of life comedy written in a 4koma/Yonkoma style. It also does not have much a plot, the main premise of the story is basically a group of girls hanging out and having fun with their club. If you prefer your manga to have a solid concrete plot this isn't the manga for you.

K-ON Highschool takes place after the original series. It stars Azusa Nakano who is now the president of the Light Music Club (Pop Music Club in the official manga translation) and how she has to get new members and continue the legacy of the Light Music Club.

Ui Hirasawa and Jun Suzuki, her friends from the previous series, have already joined the club and the 3 of them need at least 1 more member to make sure their club doesn't get shut down. (In Japanese schools you need at least 4 active members in order to be considered a club.)

Thankfully, they are able to find and recruit two new members: Sumire Satou and Nao Okuda. However, the two characters don't have any musical experience before joining so the new Light Music Club will have some unique obstacles in this manga.

While the general tone and humor are very similar to the original series, with a brand new set of main characters (Azusa and Sawako aside) this series is able to create its own new and unique funny quirks and jokes without copying a lot from the original series.

Azusa is the serious one who wants the club to always be practicing, Ui is the very caring and responsible one, Jun is the somewhat lazy one, Sumire is shy and nice but has a goal of wanting to get back Mugi's old tea set and Nao is the stoic one who is really good at studying. Sawako is still the same lovable adviser with a love of cosplaying.

The group's dynamic and interaction is different enough from the original series to not feel like a total clone of it. Regardless, the interaction between the main characters is amusing and very enjoyable, just like the original series.

The one main flaw I have with the series is how short it is. The series covers 6 months of in-universe time in 14 chapters, which isn't bad at all. However, unlike the original series where you have 50+ chapters to get to know the 5 main characters, I feel like the series could have at least 10 chapters longer.

This is especially bad for the new characters Sumire and Nao. While they are very likable characters and you get a basic feel of their personalities, I feel like I could have gotten to know them even more.

Despite that, this short sequel was quite enjoyable for what it is.

If any of the following apply:
A.You liked the original series
B.You wanted to see what happened with the Light Music Club after the main series
C.You just want a manga with fun happy times

then I highly recommend this manga.