SHR is just a friendly gui to automatically juggle mdraid arrays to fit when you have different-sized disks (e.g. if you have 2x8 TB disks and 2x10 TB disks, SHR will create one 4-disk 8 TB mdraid array and one 2-disk 2 TB mdraid array and append them to a single volume).

The one proprietary bit Synology has is a way to use mdraid parity to fix checksum errors detected in BTRFS.