expansion means external expansion HDD
expanding memory
Backuplus support removable cardslot i.e. its card can be detached from HDD and can be used with any sata 2.5 hdd. expansion hdd is factory sealed in casing. I have seagate as well as dell backup plus usb3 hdd and they perform well. Will be getting Adata drive next year.
Go for Adata A710 a shockproof and waterproof HDD thori costly hai
http://www.flipkart.com/adata-dashdrive-hd710-2-5-inch-1-tb-external-hard-disk