My setup, UNAS and Mac Mini M1, with 10Gbps networking, will easily perform as well as the NAS in question, but the Mac Mini only uses 4.6W idle, making it much more efficient.

As for ZFS vs Btrfs, they're about equal unless you're doing some very specific things. For most normal server stuff or NAS stuff, Btrfs is every bit as competent as ZFS. Snapshots, compression, RAID1+, recovery, bitrot detection, they're pretty much equal. ZFS as an advantage with RAIDZ1/2 as Btrfs apparently hasn't managed to make RAID5/6 stable in the past decade. You can however run RAID1 across multiple devices with multiple copies, which is not quite the same, but also not terrible.

The RAM usage of ZFS is also largely a myth. Yes, it will use RAM if available, but that is mostly because it was designed with it's own file cache, which was probably fine on Solaris, and to some extent on FreeBSD, but Linux uses a shared block cache, and instead of files being cached in the shared cache, ZFS will cache them, making it look like it hogs RAM.