I certainly recognized several Mercurial features and concepts in Sapling.
For example, I use Mercurial’s absorb command [1] and was pleased to see it in Sapling.
Overall this looks promising.
[1]: https://gregoryszorc.com/blog/2018/11/05/absorbing-commit-ch...
Absorb is amazing! Even if you don't take up Sapling, there's a 'git absorb' plugin which I have found absolutely invaluable: https://github.com/tummychow/git-absorb