I tried Free File Fillable Forms last year on principal, but I ran into issues in two areas:
1. reporting scholarship income (goes on the line beside box 1 and nowhere else), and
2. state taxes are not supported, and my state does not have an equivalent service.
It's really frustrating that states have not adopted an equivalent service. I actually filed paper forms for mine because their free service is a simplified approximation of the full form and leaves out certain workflows that limit its scope of complexity.
1. reporting scholarship income (goes on the line beside box 1 and nowhere else), and 2. state taxes are not supported, and my state does not have an equivalent service.