What makes a good spaced repetition system? (jpdb.io)

I recommend reading yesterday’s post discussing my follies with WaniKani the first time I tried learning Kanji. Over a year and a trip to Japan passed before I made a serious effort at studying Japanese again. WaniKani had failed me in several ways, and I was reluctant to try a spaced repetition system that wouldn’t solve them. I wanted something that would adapt to my existing Japanese knowledge,…