I use it occasionally and trying to port an old Gtkmm toy project to Gtk-rs was an eye opener regarding both build performance and the pain of dealing with callbacks in GUI code.

First having neither a build cache, or binary dependencies, means that C++ wins on the "make world" build, because naturally all my third party libraries are already compiled.

Then there is incremental compilation, incremental linking, pre-compiled headers and modules to help with the rest.

GUI code then becomes a fest of Rc<RefCell<>> in event handlers, or using arrays with vector clocks workaround as shown on Catherine's talk.