I use it as my laptop's root filesystem. It works well for me. Here is a link to notes on how I installed it:
Honestly, I recommend XFS over ext4. It seems to be a much more mature file system, and Redhat-family distros (RHEL, Centos, Scientific, etc) have switched to XFS as the default filesystem (instead of moving to ext4 from 6.x's default of ext3; 6.x does not support XFS or ext4 for root).
XFS performs better out of the box on a wide range of hardware, while seemingly giving stronger data reliability guarantees (but not anywhere near ZFS's).
ZFS on a single disk, however, will still give you data checksumming, so you can detect silent data corruption. XFS's sole missing feature as a basic filesystem, imo, is data checksumming.
RHEL6 uses ext4 as default[1] filesystem. It certainly does support ext4 as root.
[1]: https://access.redhat.com/documentation/en-US/Red_Hat_Enterp...
The compression and deduplication features of ZFS is terrific on network filers. Compression could possibly improve performance slightly on a single disk system.
With two disks, I'd say you'd probably be better off with running RAID0 (or no RAID at all) and having a great backup plan. Using another SSD to cache writes to another SSD doesn't make a whole lot of sense to me.