There are three one-shots here. Two are follow-ups to Kimi ga Suki, and one is much longer and completely unrelated... and that's what I'll mostly focus on.
First, to get the Kimi ga Suki follow-ups out of the way. Both are fine. One tells the story of Aki trying to win the approval of Mase's possessive and manipulative older brother. It's a little creepy, but ends well. The other just talks about Mase's quest to be more intimate (physically and emotionally) with Aki... and it's about what you would expect. If you have read Kimi ga Suki and like the characters, by all means, read these two chapters; you'll like them too.
The final one-shot is completely different and completely unexpected. It starts off with a tsundere-ish couple of kids in an orphanage who are reluctant to admit their feelings for each other as they grow from "protective older boy" and "crybaby younger girl" to "boy and girl who like each other".
But then the girl gets adopted away by some distant relatives and she gets sexually assaulted by her new "father" and suddenly this isn't the manga that I thought I was reading. I won't disclose any more of what happens, except to say that it does all tie together.
The end result is a very complicated manga that brings up some very disturbing issues. I won't say it's a great one-shot--I think it sugar-coats things just a little too much to be great--but I certainly applaud the attempt. And I have to say, I was shocked to find something that serious and important tacked on to the end of a couple of sequel one-shots to a fairly short and fairly mediocre shoujo romance.
