Only watch this OVA if you have seen the anime, otherwise you won't get anything out of it.
IMO too much time was wasted on Ryouma's filming -- generally I find that OVAs that follow a single manga chapter or two are wasting too much time on irrelevant things that make sense in the progression of the manga, but make the adaptation have less impact than it could.
The twist is excellent, and really got my hopes up for a moment -- I complained about stereotypical roles in my review of the anime -- but then the creators went right back to stereotype, so this was rather meh for me. Maybe it's heartwarming if you love these characters, but I never invested that much into them.