Outliners are great and underrated tools. But after a detailed analysis of Org Mode (and some other tools) I implemented https://github.com/rochus-keller/CrossLine which I'm using every day since ten years.
I wouldn't say it's "better"; it just has some features which I didn't find in other tools at that time, e.g. translucent cross-links, everything in one fulltext-indexed file, immediate incremental persistence, not speed-down for large outlines, dockable outlines, just to name a few. Didn't have a close look at Org Mode since.
EDIT: of course there are many features which also Org Mode has, e.g. extremely efficient to operate by keyboard (for a trained user), multiple outlines, titles, attributes, not wasting screen space with menu bars and the like, just to name a few.
Org-drill is technically good for this, but ask yourself - when do you actually sit down and revise something? At your desk? In public transport? In the toilet?
If like me the answer is the last two, then stick with Anki. Much more portable.
