>>SpaceM+bh1
https://www.supermemo.com/en/blog/supermemo-is-better-than-f... seems to suggest that yes, it is a major improvement over SM-2, and given how critical they are of FSRS I'm happy to believe them. SM-2 to my understanding is basically the simplest possible spaced repetition algorithm - I think something like 'double the review interval if easy, otherwise multiply by some difficulty factor to reduce this interval depending on which button was clicked'.
That said, even SM-2 is probably vastly superior to just not doing SRS at all.