Safepoint - Recommended Devices for Safepoint Creation

I am seeking recommendations for an external USB device that will work well with my My Cloud 3TB external storage device.  I am currently using approximately 500GB of my 3TB.  I am thinkining that I would want a device that offers at least 2TB of capacity (to accomodate increased consumption of the free space on my My Cloud).  Perhaps a My Passport Ultra 2TB or if I’m living large, perhaps the My Passport Ultra Metal Edition 2TB?

I purchased a WD refurbished My Book Studio 3 TB … the only caveat is a shortened warranty to 6 months.