Is Delta Epsilon Iota a legitimate honor society to join?

Don't bother with it. Most college honor societies are a waste of money, and I say this as someone who's a member of 3. The Golden Key is plenty...I actually regret spending money on joining it, but if you want to be part of an honor society, I would leave it at TGK. Unless the honor society is very selective about who it admits, they won't really give you a leg up if and when you apply to graduate school. In my opinion, it is all too easy to pad your resume with various college honor societies, and I would think employers see right through that.