[mvieira38]

Also, why SM2 instead of FSRS?

[bpev]

Probably simplicity. In my experience, SM2 has less levers, and is easier to implement initially.

[jarrett-ye]

SM2 has less parameters, but there is not a systematic way to tweak them correctly. With the optimizer, it's easy to make FSRS adaptive to any learners. There is only one lever for user to tweak in FSRS: the desired retention.