We use those APIs internally to implement Sharp Cells. You can certainly build your own integration however the XLL API in particular was poorly documented and

We use those APIs internally to implement Sharp Cells. You can certainly build your own integration however the XLL API in particular was poorly documented and very difficult to implement correctly. Sharp Cells' aim is to make it easy to use these APIs from F# so you don't have to worry about P/Invoke, manual memory management, dynamic .NET assembly loading, etc. to just write custom functions.