So after a little experimentation, I've come to a bit of an impasse.
I've been trying to render a pie chart for a little while, and it seems that I can only persuade the SfChart (currently looking at Xamarin.Forms on Android) to render when the Content of the page is a vertically oriented StackLayout, and the SfChart is a direct child of that StackLayout.
Any other situation (eg. a Frame, or inside nested StackLayouts, etc.) results in either nothing showing at all, or just the SfChart Title being displayed.
Is anyone else having better luck?