FxCop was analyzing IL to come up with suggestions to code smell (which very much broke down when the compilers started generating state machines for eg async/await). Roslyn-based analyzers do this on source code. Thus they work great in finding code issues.

That is one part of Refactoring Essentials. The other part is refactorings, and yes, that is very much like Resharper. (StyleCop is not something we do today)