My experience is kind of similar. Unfortunately the way Rust interacts with memory is quite different from how Gtk does (and most GUI tool-kits to be fair). The end result is a kind-of awkward battle between the Rust borrow checker and the internal memory handling of Gtk+ leading to loads of Rc<RefCell<T>>. This makes also quite hard to implement custom Widgets in an intuitive way. In Python or C++ you would subclass the generic "Widget" class and start implementing the bits you need. With Rust things are slightly complicated; you can't just implement the IsA<Widget> trait and call it a day; at least not a straightforward way. Hopefully gnome-class [0] will probably solve this problem eventually.

That being said it's been a while since I've used gtk-rs so it is entirely possible things have changed. I'd love to be corrected if that's the case :)

[0] https://gitlab.gnome.org/federico/gnome-class/