Dh is bringing me back a copy tonight, quite excited. To Kill a Mockingbird is a well-written, well-plotted book with great characters, and this isn't going to detract from that. For me it is a stand alone, this merely fleshes out some of Lee's original thinking around her subject, and perhaps layers a more complex, adult treatment of the issues in TKAM, which is, essentially, a good story for children, complete with moral.
It is a big literary 'moment', and of cultural significance if nothing else, so, yes, I'm interested to read it for lots of reasons.
I am also mindful of how problematic the publication is, regarding the situation with Lee, her sister's death, and her new legal representation. But, it is out there. For me, there is nothing to be gained by not reading it, it will not alter Lee's legacy in my eyes or lessen her achievement with TKAM, or its belovedness in the eyes of its fans IMO.