Excellent for Both Supernatural and Harry Potter Fans.
This fanfic and it's sequel read like side stories or filler episodes for Supernatural. The events technically take place within canon, but are set up in such a way that they don't necessarily have to interfere with show's story-arc. Both fics combine drama, humor, and action in a manner one would expect from something trying to stay true to the mood of both Harry Potter and Supernatural. The author does a very good job of integrating the two worlds for the most part and for the most part sticks to canon.
Readers should be aware that Damned Demented Demons takes place in an environment more familiar to the Supernatural universe while it's sequel, Vile Violent Vacations, is set mostly in locations from the Harry Potter series.
There is sometimes a rather heavy use of phlebotinum to move the plot along, but considering as neither Supernatural nor Harry Potter is innocent of the trope in any way shape or form it can be easily forgiven.