What gets labeled FDE is a very wide spectrum right now. What companies like Sierra do well is allow FDEs real autonomy to deliver meaningful customer outcomes while also making meaningful contributions to the core product.
A pivot from SWE to FDE can be an incredible move for lots of people, but make sure the company can give you concrete examples of platform/product work that FDEs have driven before joining.
"Engineer with customer facing skills" is a great pitch but only if you actually get to flex both your engineering and customer facing muscles in roughly equal measure.