Adding to current NAS

I currently have a WD My Cloud 3TB
Im wanting to add an hard drive to it as i’m close to reaching full usage on the storage.
Im unsure which to use/be better to use between a portable hard drive such as the external portable drive: My PassPort 4TB or the desktop drive: Elements 4TB Desktop External Hard Drive
I was unsure whether my the elements one being a desktop drive would it have faster speeds? therefore making it better to add to my NAS

Hi KrazyBrute,

My Passport and WD Elements Desktop, both can be used with My Cloud as they come with USB 3.0 with similar data transfer speeds and compatibility. Only the different is the input power where WD Element desktop require power adapter while My Passport is a portable.
However, My Passport comes with WD Discovery™ software for WD Backup™, WD Security™ and WD Drive Utilities™ and these would be in handy when you work on computer.