I used ZFS with Arch for a while, the volume manager was what I’d call the largest benefit; in my opinion nothing else comes close to being as useful and well integrated.

I stopped because ZFS incompatibility with recent kernels (which I needed for GPU reasons) made me have to rescue my system more often than was ideal.

Some other minor downsides:

• boot can take ages due to ZFS using udev-settle.
• deduplication status is… Complicated.
• you’re kind-of stuck with the performance of your slowest vdev; L2ARC & a metadata device don’t really compensate well for a zpool that is predominantly a raid-z2 of spinning rust.