The F-CLUE is an optical fiber-coupled solution providing a flexible interface for Cathodoluminescence (CL) Imaging and Spectroscopy analysis. Its rugged, ultra-compact design and detachable spectroscopy modules make it suitable for installation on busy microscopes or in challenging environments, such as clean rooms or mobile labs. Like other CLUE systems, the F-CLUE features a compact, fully retractable collection interface, allowing for CL upgrades on any commercial microscope without compromising performance. The video-assisted micropositioning of the mirror ensures optimal collection efficiency and reproducibility. Managed by Labspec 6 software, the F-CLUE offers advanced imaging and spectroscopy functionalities, including spectral databases, cosmic ray removal, peak fitting, particle detection, mosaics, multivariate analysis, and 3D display.