Last time, I looked at customizing Xamarin Forms applications so that the functionality is the same across platforms. I looked at the components and setting to make this possible, and added some custom, platform-specific programming to accomplish this. The result has been that my picture-taking application for my startup has rounded into form and is usable in low- and high-bandwidth areas. I've had a couple of users test it out with much success.
But that app is still missing something: On the iPhone, XF is well integrated with it. The programming model feels very much like programming against the native iPhone API. On Android, it provides a good representation of the Android UI. However, there are some basic settings in that UI that I feel it's missing.