Interesting. I am directionally opposite: half an hour of reviewing is very pleasant for me and is comparable to a much shorter period of work-work.
For me, though, improving the new-card experience and the software generally is an important part of making reviews feel pleasant and smooth. I want my spaced repetition environment to be a cozy, ergonomic corner of my world. Using nice software, and studying flashcards that benefited from a good new-card experience (so that I could write them well, include appropriate images, and so on), is part of that.
Ah! Right. Sorry for my error!
I do agree that the data are, for obvious domain reasons, not linear. If you have some reason I don’t account for to think that they’re exponential, I’d be grateful to know it.