Wasn't this supposed to be a teaser for vs. Cyborg 009? I would have preferred a Devilman remake as opposed to that, but it was still nice. I still don't know why no one has subbed it yet since its been a few months since it released.
The OVA was fairly faithful but it only covered two of the five volumes.
The Toei TV series was in production before the manga came out so it's sort of a mashup between Devilman and Maou Dante adjusted for TV airing.