Accurate enough, on the visual check it gives you. I have somewhat away-from-the-mean hands and I'd expect anything that moves their shape while typing to less bunched-up to be noticeably more comfortable.

I can test this, in fact - I'm already building a custom keyboard, although it's a) not with this generator, and b) intentionally closely matching another keyboard I own. I could do another with the horizontal spacings from this site while keeping everything else the same, and see if it's preferable.