I have a knock off version of the second one I got in an ebay bundle. It's simply called 'Dual USB Adapter'. When you plug it in, you can only press one of left or right. When you hold down select+start+up for 3 seconds it switches to a different mode.
In the alternate mode it's supposed to let your press left and right simultaineously, but rather than register as 2 constant button presses it alternates rapidly between the two. Really messes up your timing in DDR when alternating between left/right steps. Also, if I press right and left at the exact same time neither registers, so I have to stagger my landing on jumps. This really messes with your timing in DDR.
Just a warning for those thinking of buying a cheaper knockoff brand..
-Kevin