My initial use of DigiKam was disappointing. It was resource intensive and its organizational methods seems more than a little arcane. I used Shotwell, from just about the time it was released. It is pretty lightweight and organizes via time line and tags. It is fast efficient and stable, and it does have decent tools for working with meta data which is optionally saves to the files. I always saved the meta data to the files.
I took another look at DigiKam and found that easily read the meta data from the files, so it respected my tagging. It was resource intensive and it felt very slow at getting setup. With the meta data created in Shotwell it did a nice job of organizing the collection in useful ways. And almost as a bonus it did this via a database that honored the structure created in Shotwell. This meant that I could use my same pictures folder on systems that used DigiKam or Shotwell and that changes or updates done in one would be respected in the other.
DigiKam has facial recognition which is pretty good. Using tags I had created in Shotwell I was able to quickly identify a great many of the folks, and one a small set had been identified Digikam is able to do matching and again it does it pretty well. And with KDE's very nice system wide integrations, the recognized people can be tied with KAddressbook.
DigiKam is very resource intensive and it grinds away at tasks slowly, but steady. I have not moved to DigiKam as my main Photo manager yet, but I am definitely moving in that direction. I am finding it works best to make sure DigiKam is doing all its organizing and such on your fastest machine, but once all the grinding work is done one can move the "Pictures" folder and the DigiKam database (which is stored in the Pictures folder) to a lower speced device and have it run very acceptably.