Agree completely other than the functional bit (but I'm not sure if that was a recommendation or just Google keyword help). At least for Android, I've found that maintaining state when handling screen rotations etc becomes a real headache if the GUI binding code is functional (there is nowhere nice and clear to hang the state without storing it in an rxStream or similar). So far I favour reactive code absolutely, and functional (ish - I'm still using DI for example) code right up to the view layer, but then drop out for the last mile of data binding