The latter two are branded as "Canvio Plus," but the only variation seems to be in storage, dimensions, and price. The smaller two measure 3.1 x 4.7 x 0.53-inches and weigh 5.2oz, while the larger drives are 0.12 inches thicker and 1.1oz heavier. All of the drives use USB 2.0 for data and power, are available in five different colors (blue, green, red, black and silver), and ship with a three-year warranty.
In addition to being "pocket sized" the drives come with easy-to-use backup software, which has improved search capabilities, simpler step-by-step restore functionality to retrieve lost files, and brings more features for advanced users.
It's worth mentioning that the company links an interesting poll on the Canvio product page which shows that Americans are more afraid of losing irreplaceable documents than having a wallet stolen, being audited by the IRS, or even losing their job.