Watermelon is a great replacement for stacked Pull Request tool such as Graphite.
Stacked PRs a practice popularized at FAANG companies that consists in splitting big PRs into self-sufficient, smaller ones. While dividing PRs as much as possible is something good to do once the anti-pattern (a huge PR) exists, it's a solution to a problem that shouldn't exist in the first place. They are something very unique to FAANG companies.
Tools like Graphite, first, require you to learn a whole new git system which implies a huge behavioral change. Second, stacked PRs won't help developers asses whether a PR meets or not the business requirements.