That depends on the license, in my understanding:
- Dirac Live with the basic license (stereo or MC) is doing FIR-based EQ on each channel, which apart from fixing the frequency magnitude response (EQ) also tries to make the impulse response look pretty.
Frequency magnitude response correction can be done manually with REW-calculated filters, and you could also manually calculate a similar phase/impulse correction with e.g. rePhase.
However, as I mentioned before, research seems to indicate that the shape of impulse response is perceptually largely irrelevant (within reason, of course) - I refer to this article by AudioXpress for a bit more information and references, as well as opinions by several authorities in the audio field.
I also couldn't hear any benefit of phase/impulse correction so I don't bother with it.
- Dirac Live with the additional Bass Control (DLBC) license enables optimization of multiple subwoofers and loudspeakers to provide a smoother bass response over a wider area. I suspect very similar results could be obtained manually with the Multi-Sub Optimizer (MSO) free SW.
- Dirac Live with the additional Active Room Treatment (ART) license uses all channels (satellite and sub) to reduce decay time in the bass region. To my knowledge nothing similar can be done with free SW, but I have no experience to comment how well this works or whether measurable improvements translate into audible benefits.
So as I see it, if you have the required competence you can get similar results to 1. and 2. above with free SW. Note that it will not be identical - but two calibration passes with Dirac Live probably won't be identical either so I don't believe that is worth fixating on. With REW you definitely have more control which is something I like, but it is also why beginners may feel overwhelmed (I know I have!).
But automation is huge value - not everyone is willing to spend the time to learn and understand the manual process sufficiently to get consistently good results. Dirac is simple to use, allows tweaking so you can adapt the response to your preference and works really well in the process. I can absolutely understand people who buy it, especially if they don't view audio reproduction as a profession (or a serious hobby)!
There are many examples in life where we prefer to pay someone else to do the work, rather than spend our time to learn and do the same thing to save some money - this is not that different!
Lastly, in any kind of engineering there is rarely only one correct answer to any question - it is the same in audio engineering.
Asking questions online in a forum can be useful and may give you some ideas, but without a deeper understanding of physics/technology/psychology it can be next to impossible to decide which advice is perfect and which is less so for your specific situation.
However if you are an audio enthusiast (and you probably are if you are here asking questions
) it may make sense to attempt to learn the basic concepts to see where best to invest the time in experimentation and to allow you to make more informed decisions down the road.
My go-to recommendation is the amazing "
Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms" 3rd Edition by dr. Floyd E. Toole.