While Let's Talk Tech was "quite surprised to find that the drive wasn’t as slim as the name suggests," Laptop Magazine says it's still "mighty thin and light." The PC Enthusiast finds it "easy to carry around and very portable." However, being thin doesn't mean it's fragile, as Computer Shopper notes it's very "solid-feeling" thanks to its "rigid metal shell," which CNET calls "very sturdy in the hand."
The Slim also boasts pretty reliable speeds, which The PC Enthusiast found acceptable "considering its portability." Computer Shopper says "It’s reasonably quick over USB 3.0," and over USB 2.0 CNET calls it "the champion."
Western Digital's My Passport Slim doesn't offer a huge speed or size advantage over its sibling Ultra, but for a few extra dollars it does offer a little more security in the event you should bang it or drop it on the floor, thanks to its tough metal enclosure.