I've used FreeTaxUSA for many years and never had a problem. I now work for one of the major tax prep companies filing other people's taxes for money, but I still used FreeTaxUSA to complete my personal tax return. It works great for the vast majority of people. But if you have a complex return or an unusual situation, you might want to hire a real person to file your taxes for you.
One year I worked a temporary job in the summer and the company erroneously withheld taxes for the wrong state. Using FreeTaxUSA I wasn't able to figure out how to file a nonresident return to West Virginia to get back the money erroneously paid to them. That was an unusual situation, and the software couldn't handle it. But other than that, it's always worked just fine. I don't mind paying $12.95 for the state return because it's still a lot cheaper than any of the commercial tax prep stores.