Although Hel is ruler of the underworld and a "destroyer" Goddess, She is not to be confused with the Christian devil any more than is the God of the Wood. 
     As Freya is the Keeper of souls who died in battle, Hel is the keeper of souls that did not. To the Vikings, dying in battle was the most honorable thing that could happen. Thus, the phrase "Go to Hel" was probably meant as an insult of dishonor. The additional "l" was possibly a Christian addition to make everything fit with their mythology.
      Hel can be a kindly crone type or a fierce destroyer. At any rate, She is a powerful Dark Goddess and deserves much respect. Hel is a useful and powerful force to rid your life of obstacles. But do beware! Hel may well  cause change by total destruction! Hence the phrase "Blessed Hel Fire". 
     Call upon Her with respect. Call upon Her with caution. Call upon her with confidence. "Raise Hel" during the dark of the moon and see results!