Having recently begun training in Tae Kwon Do (and loving it) there is an amazing amount of gear that needs to be purchased to be able to fully participate in class or practice at home. These hand targets were purchased at the class I study at, but I found similar brands/ targets at Amazon for about $20.00.
The purpose of the double target is pretty self explanatory- you hit it! With an elbow, hand, foot, or knee and the poor sap you got to hold it for you tries not to let the thing fly out of his/her hand on impact. The beauty of this particular design is that they have a wrist strap which will prevent the target from striking a near by participant if the person holding the target loses their grip.
The "double" part of the target refers to the two cushions placed side by side instead of one big solid soft sponge. These dual layers are completely independent of each other therefore allowing the target to make a slapping noise if the hit is executed correctly. A hit off the center mark will make a different sound all together usually punctuated by obscenities coming from your training partner.
With the logo as large as it is and placed directly on center, you can really work on your aim, not only within the bounds of the target itself, but also within the logo design. Kind of like a bulls-eye. If you purchase a target from another source/brand name I highly suggest creating your own target marks as it really does help.
My only negative remark on these is that the frame seems to be somewhat easily bent, I may purchase a back up set just in case.