There are some poorly made APIs, like ASP.NET MVC that exploit C#-specific side effects to compensate for C#'s verbosity. These APIs ignore the common type system and just pass object everywhere, breaking tooling and type safety.
But as long as Xamarin didn't come up with terrible designs, you're all set. And, even if they do rely on something strange, F# is such a better language, that the small setback of dealing with interop (which doesn't require learning C#) is totally worth it.
open System.IO // F#
using System.IO; // C#
let thing = new Thing(a,b,c) // F#
var thing = new Thing(a,b,c) // C#
Console.WriteLine("blah") // F#
Console.WriteLine("blah") // C#
Essentially C# parameter lists become tuples in F#. So interop is mostly quite straight-forward. It's mostly quite a mechanical process to convert C# sample code into F#.It's harder to go the other way, and take F# code into the C# world, because functions in F# allow for partial application. The type inference system is awesome, so you'll end up with more generic functions and use first class functions more. That stuff is tricky to bring back (though not insurmountable).
The OO grammar is a little tricky in F#, but I tend to shy away from that. It's not needed most of the time.
Then at least you don't have to deal with all the stuff this library is trying to solve ;)