1. That picture of the dark dragon is large. Very large. Especially compared to the not-large light one.
2. I've been toying with them in Chaos Dragons since the day they were put on DN and I love them. They provide solid grave management, a decent sort of advantage engine, provide better access to Queen Dragon Djinn, and allow for techs like Enemy Controller or Caius to be used to great effect.
Also been pondering them in a Monarch-ish deck, but haven't tested the build I came up with.