"Pretty fast".. relatively speaking, considering that it's in an immutable, garbage collected language. Still woefully slow compared to anything else out there(say, bevy? which incidentally works similarly to apecs) and mostly practically unusable if the goal is to actually create a real product.
You can create a real product with apecs lol. It is not going to block an indie game written in Haskell with it, for instance. And you could totally use it to write simulations for stuff too.
Also from the apecs README:
> Fast - Performance is competitive with Rust ECS libraries (see benchmark results below)
Sounds like that "woefully slow" judgment of yours wasn't based in any real experience but rather just your opinion?
Want to just have fun? Sure.