Searching through the repo [0,1] it seems like you still need to write a certain amount of C++ especially if you're using QtWidgets instead of QML. So in my eyes this seems like a way to incorporate Rust code into a Qt project rather than build a Qt interface for use in Rust, as the end program is essentially a C++ program with some Rust bits.
From what I understand if you have a fair amount of existing Rust code to reuse in a Qt GUI application this is probably the best way to get them to talk together but it's a still a bit far from "Qt GUI for your Rust programs". I get that the distinction between the two is a bit blurry but in any case you still need to write a considerable amount of C++ especially if you opt for the QtWidgets way.
Of course it is entirely possible that I've completely missed the point so in that case please correct me.
[0] https://github.com/KDE/rust-qt-binding-generator/tree/master...
[1] https://github.com/KDE/rust-qt-binding-generator/tree/master...