Rather than securing the phone using velcro, this design relies on a flap covering the opening to where the phone sits which means you're relying solely on compression against your arm to stop the phone from falling out while running. It's also clearly not waterproof and, because of the flap, getting the armband to sit nicely is a little awkward. In addition, even with a case on the phone doesn't fit snugly into the armband and can more around inside its compartment, implying that whoever designed it didn't pay too much attention to the phone's dimensions.
To top it all off, the hole for the headphone jack is in completely the wrong place. Having previously had a very simple and effective velcro armband from iGadgitz for my old phone, this particular item was disappointingly poor.