Despite being a huge fan of Subaru and Seishirou, I never got around to see the OVA up until now. It's an extra story for the ones that read the manga and has two pretty good episodes, but can never reach the level of the manga. The bond between Subaru and Seishirou are almost non-existent in this adaption. It's fun to see the characters coming to live in early 90's setting. And to see Subaru and Hikoto wearing their various (flashy fashion) outfits of the manga in the anime. Overall, the two stories were interesting as a stand alone, but nothing too special.
If you are a huge Tokyo Babylon fan, see this episode. If not, just read the manga and you'll be happier. Or watch some episodes of Tsubasa and X if you want to see Subaru and Seishirou come to live in anime style.