The difference is that instead of being a "wizard" interface like other tax software, it's just online fillable versions of the tax forms, that do 99% of the math for you based on the values you enter and automatically add forms and link values between forms as necessary.
I've used it for well over a decade, and at the end of the day it's just the same "doing your taxes" that my parents and grandparents did, but on your computer and easier. For anyone who has an engineer mindset it's entirely doable, even if you have to Google a few things to make sure you're doing it right (e.g. what's a qualified dividend vs. a regular one?). The real secret is keeping a PDF of your previous year's return next to you while you do this year's, because you'll usually just be filling out mostly the same lines in the same way with different values.
[1] https://www.irs.gov/e-file-providers/free-file-fillable-form...
[2] https://en.wikipedia.org/wiki/Free_File#Free_File_Fillable_F...