The OVA takes place in two different parts in the anime. The first half takes place after S2 episode 2, but the last half takes place after S2 episode 5. So essentially, if you want to watch this it is best to watch after S2 Episode 5. The first part goes over how Shiraishi became known as the Escape King. This covers chapters 84 and 85 and is very well adapted.
While the 2nd part introduces the Saksomoayep from Asirpa talking about Ainu culture. This one adapts chapter 104, but the issue with this one is that it served as a great piece alongside what will be in the chapters that cover the 5th OVA. By itself it is fun. However it loses the reason for Noda writing it in the first place without the contents of the 5th OVA.
Is this worth watching? I do think this episode is a huge improvement over “Monster” As I mentioned, it talks about Shiraishi’s origin story. Which is very fun and definitely worth a watch if you love the characters in the anime. Now, do note that Kumagishi is cut out of the main anime since they cut out the Fake Ainu Village Arc. This side story is fully skippable because of that, but if you have loved the series so far, you should watch this episode of the OVA as well.