I'd like to know what other real world use (besides learning new words) did you use spaced repetition for ?
EDIT: I would appreciate if you could pick a specific example go into some detail and describe the experience
There's also https://github.com/axelboc/anki-ultimate-geography a deck covering all countries, some overseas territories and oceans, which is what made me start using Anki for geography.
For things like flags, counties, etc. it works great - I can now recognise more or less every flag in the world and the total time allotted is probably less than an hour.
For things like vocabulary, historical facts and especially programming language stuff it's not quite as useful - a little bit of context helps here to really cement these concepts in memory and spaced repetition doesn't work as well when what you are remembering is less "atomic". It also makes it harder work and less fun - this is a sign that you are stretching yourself a little of course, which will pay dividends if you put in the effort. It does make it more of a chore though. Overall, it's still a time saver.
One thing I've noticed using Anki is that I often find myself struggling to remember something the other way round. E.g. I will have learned a word X (front of the card) with definition Y (back of the card), but then I find myself at some point in life trying to think of a word with roughly definition Y and I can't quite remember the word X even though I'm aware this is something I've put into Anki. I think I might try doing cards both ways round but this can introduce some complexity since a one -> one mapping can then be many -> one when reversed (at least with English vocabulary, might work better with other things).
Subjectively, I am finding it pretty effective at helping me understand how all the systems fit together. It's easier to understand a codebase once you have context of how everything fits together.