Digikam
Useful settings
Collections -> Ignored Directories -> #recycle
Metatdata -> Use Lazy Synchornization: makes you confirm the changes before writing them below. Useful when working on lots of pictures (eg face recognition)
Metadata -> Sidecars -> write and read on.
Miscellaneous -> Behaviour -> Scan for new items at startup, fast scan, detect faces in newly added images
Faces
In the preview you can select show face tags on and off in the top left of the preview picture