Yui was feeling creative someday and she decided to draw some random funny stories about the Keionbu. This is Ura-ON!!~
Imagine that a friends of yours badly drew short funny stories about your group of friends and then showed you and you laughed together, sometimes at the jokes, sometimes at the retardedness of the story and sometimes at the really bad drawings.
I think that thinking of it as this will make it more enjoyable. Really, don't take it seriously! The intention is to be retarded fun! Maybe if you make sure to be in a retarded state of mind when watching this, you can enjoy it better.
So, having used enough the word 'retarded', let me summarize what is this.
These extras are funny short episodes drawn in MS Paint-like artstyle. There is no storyline, each episode has its own random theme, for example, cooking, siblings, souvenirs, etc.
I think I just LOL'ed at the most of it, but I really laughed at some parts (episode 4 specially), and, well, badly drawn it is, but there are the characters you must know well being themselves together.
I watched this because I wanted something light-hearted and funny like K-ON, so I'd recommend it to a K-ON fan also looking for this, even if only for the lulz.
(This is my first review, so please be nice to me ;-;)