Having been building a decent size app (tens of thousands of lines) in Xamarin this really reflects our experience. One particular point is that the memory management is fairly complex under the covers with bridged objects and multiple memory management mechanisms working in parallel, this occasionally rears its head.

Another important point is they do provide a single automation test framework that targets both platforms.

If I was starting the app again I'd be very conflicted whether to use Xamarin vs native, though ReactNative looks very interesting too and doesn't have the complexity of running the full .net stack.