I've used TT since 1999 for my own (relatively simple) returns, and have always liked it very much. Makes doing taxes kind of fun!
When my father died in 2000, he had been having his returns prepared by an accountant he had worked with for several years because of some more complicated investments, real estate, etc., but he basically did all the prep work for him putting the necessary data on spreadsheets for the various schedules, etc., so the accountant just had to put it into his proprietary software. It still cost beaucoup bucks, though! To help my mother, I continued to prepare the tax information in the same way for the accountant for 5 more years, which now included preparing a Family Trust return as well as the regular individual return (which even made the accountant fee more expensive). in 2006 I pulled the plug on the accountant and just started doing both my mother's returns myself as it was a lot (over $1000! by then) and I was doing most of the heavy lifting anyway.
However, I have to admit if I hadn't had the previous years of accountant-prepared returns as a cheat sheet/reference, I think it would have been very hard for me to complete the Trust return on my own (it's a separate TT product you have to buy for it). I even considered using TT's paid live-person checking service for the first year of doing it, but in the end was too cheap to do so. I have to admit I expected the IRS to haul me away in cuffs for making some fatal inadvertent error. That hasn't happened yet (6 years in), so I assume I'm not making major errors.
So basically I agree with RE2Boys that while easy to go through TTs questionnaires, unless you actually study the forms that TT spits out to see how everything is connected, or had prior experience doing the returns with paper and pencil, it is a bit of a black box. I feel reasonably okay with my understanding of what's happening with the 'regular' individual returns, but the Trust return, generation of a K-1, etc., largely remains a mystery.