I vote legit, with the caveat that I wouldn't necessarily use it yet, until it stabilizes a bit and gains a little better acceptance/penetration.
The "first grader" explanation is that essentially it's currency that is all digital. No paper or anything exists that backs it, only digital records of how many coins are owned by which wallet. What allows it to work, however, is that the entire transaction history (block chain) is available for verification.
The security at work that prevents issues is a variety of methods of encryption that allow transactions to be digitally signed by the involved parties in such a way that they are relatively easy to confirm, but computationally infeasible to
fabricate.