One thing that bothers me is this section: Most existing software follows SuperMemo in using an expanding spacing algorithm, so it’s not worth worrying about; as Mnemosyne developer Peter Bienstman says, it’s not clear the more complex algorithms really help32, and the Anki developers were concerned about the larger errors SM3+ risks attempting to be more optimal. So too here.

None of these people criticizing SuperMemo have actually used it (as far as I know, or if they did, probably a decade or two ago). I know lots of people that have switched from Anki to SuperMemo with way better rep loads. If you look at supermemo.guru and any of the writings of the creator, it's quite clear he knows what he's talking about. It would be pretty insane that over 30 years of research, he couldn't come up with a significantly better algorithm (currently sm18).