I'd say the worse your setup (especially your room) the more magic it does.
I did it without an individually calibrated mic though (but with a decent measuring one), wonder how much better it could be.
The results are very good. I have studio monitors and a crappy room setup, and the calibrated sound is much better. I purchased the kit with the supplied mic.
That said, the software is unstable. To the point of uselessness. It caused so many system crashes that I - very sadly, because the results are so good - just don't use it anymore.
Hoping they fix stability in later versions so I can go back to using it.
A bit sad, because it might do most for less expensive speakers and untreated rooms.