I check Standard Ebooks regularly and primarily get my public domain stuff from it. It is slow to get new content, but that's just the price to pay for free volunteer driven content.

The Ebooks are really well formatted and consistent. They've even got copies formatted especially for kobo readers. I don't actually know the difference between epub and kepub myself but it's nice to know it's meant to work with my e-reader.

I know there's some kind of small drama about the more technical aspects or style guides the volunteers are supposed to use, but whatever that is it's never impacted my ability to read the books or caused obvious breaks in the visuals.