The reason why there are two different versions (Debian and BusyBox) is because there are two different single bay/single drive My Cloud version that each use different hardware. The older generation My Cloud with the v3.x/v4.x firmware uses Debian. The newer current generation v2.x single bay units with the different hardware use Busybox. Stupid using different incompatible firmware for the same device? Yes. Much confusion with the firmware numbers and which is the latest? Yes.
If you haven’t see the following thread you may want to read through them if they apply to your My Cloud version.
https://community.wd.com/t/clean-os-debian-openmediavault-and-other-firmwares/93714
https://community.wd.com/t/synology-os-on-wd-my-cloud-new-hope/95650
One of the unbricking procedures (by user Fox_exe) apparently uses a USB boot drive on the second generation single bay My Cloud units to unbrick:
https://drive.google.com/file/d/0B_6OlQ_H0PxVQVhnLVJOdDZISUU/view
