Bittorent sync comes to mind when syncing two NAS. Unfortunately it isn’t as easy to install on a My Cloud as it is on a WD ex2. On an ex2 you just need to download the app.
On the my cloud you will need to follow the procedures as laid out by this link
If you don’t want to kill your warranty by SSH’ing into your My Cloud, you can probably use your PC/Mac to sync your files between the two locations. I am using a software called “Beyond Compare” that compares two directories, once you have mapped the two Clouds to your PC/Mac, for differences and copies only the changed files.
Good luck
