Before you pack up your WD and return it, let's talk about Copying Speeds!

I have my Cloud attached to my router and an external HDD attached directly to the Cloud and… speed reads 604Kb/sec.

Don’t plug the USB HDD into the MyCloud.

Even WD recommend that, for bulk data transfers, you plug the USB HDD into the PC, and transfer files via the PC (it’s in the manual, in Appendix B, p113).

The USB port on the MyCloud might have USB3 compliant hardware, but the processor cannot transfer data at anywhere near USB3 speeds.