it's ready to use without any set up, it does not require you to install extensions, it functions on the bare minimum permissions

It's newer than mihon which is built on tachiyomi and the reading experience at the end is similar, but even then I think that kotatsu is currently more of a rounded experience

Few things I noticed:

1. Better interaction with manwha and reading alongside manga
2. Better manga downloads
3. Better notifications for new releases
4. Easier to distinguish between who released in aggregators
5. Easier to find alternatives for manga on different sites for official releases, better sites, or on the direct fansites
6. Decent recommendations from different sites and what-not, where I found some interesting manga
7. Focuses more on the manga in question more than the source of where it's coming from
8. Allows for manga sites with accounts to be able to be logged into, allows you to use coins and what-not that way

Also, some things that it js worse than mihon/tachiyomi at:

1. If you have uncertain internet then it'll hang on loading even though you have the entire manga installed to the drive, which doesn't happen when you're offline
2. Slower updates on f-droid, so patches may come later
3. Less of a community, less people to help with making kotatsu work with sites, so smaller sites are less focused on
4. The reading progress isn't as accurate, and may show 0% on manga that are up-to-date, 99% on manga that are done, and 100% even though there are still 3-4 chapters remaining

Kotatsu:

Mihon: