The U360's is basically a control pad for the PC but highly customizable since it can do 2 way, analog, 4 way, 8 way etc. It also has the ability to connect buttons directly to it and it will work the same way as pressing buttons on a PC control pad. The i-pac is different since it works like a second keyboard. The inputs are keyboard presses. The U360's buttons are control pad button presses. They're not the same.
You can go with the U360's button inputs but you'll need to buy the wiring harness for it. It doesn't come with it. And its only limited to 8 buttons. It has a shift option though.