I use the Free Fillable Forms and have done so for years. It is some of the most user-unfriendly, archaic software I've ever encountered, sort of like if you put a caveman or woman in charge of developing the program. Anyway, my return gets rejected at least once more often than not. This year, it was rejected on the basis of incorrect AGI. Now I had made an error last year and then filed an amended return. I provided the correct AGI from the amended return, but nope, the IRS apparently wanted the initial incorrect amount, which does not seem logical to me, but when I provided that number, my return was accepted.
I feel very strongly that I should not have to pay for software or a service for filing our reasonably simple taxes, even though this sometimes feels like an exercise in self-punishment.