I've always done my own taxes. The last two years I've used FreeFileFillableForms. Unfortunately, even though FFFF has a "Do the Math" button, it doesn't always do the math, especially at critical points like actually calculating your tax. I've had to supplement it with a few self-created Excel spreadsheets. For example, the Schedule D Tax Worksheet is essential. I also lean heavily on TurboTax's forums when I have questions. (On Quora, you just get a lot of "Consult a Tax Attorney")
Two reasons I don't use TaxAct or TurboTax anymore: 1. I hate trying to figure out where in the "interview" to enter something that I know needs to go on a particular form, and 2. when a number appears on a form I want to know where it came from. I've found subtle errors in just about every free online tax software I've used, and sometimes it makes it unusable, or gives me a false sense of correctness. To be fair, these were on some pretty obscure situations.
As to the question, "How hard is it", I would make an analogy to other DIY projects: changing the brake pads on a Camry, or installing a new electrical outlet. Anyone can do these things, but it is very important that they be done right. You must read all the instructions, watch all the YouTube videos, and always assume that the Dunning-Kruger effect is in play.
Most importantly, you must understand what you are doing. You are not adding this, subtracting that, and finding the lesser of these two numbers. You are actually calculating something that means something.