In most cases, less efficient than a conventional disk. Must write twice. For 10 disks, add 4 ECC disks. Performance is same as L2, but per-disk performance better since we are using fewer disks. Level 4 Same as Level 3, but use sector interleaving instead of bit interleaving.
Reliability is still good.
Overhead is still one check disk per group. Large writes are still fast. Level 5 Same as L4, but stripe parity across all disks. Reliability is good.