A:Answer If you are only planing to use an Xbox One X with this monitor and not a "High Power" Gaming PC, then there is no reason to get the Alienware 240Hz monitor. The Xbox One X only support frame rates up to 120Hz, and even this frame rate is newly supported by Microsoft and not many games yet support 120Hz from what I understand.
With that said, to answer you question, the 2 monitors do not compare to each other. The Alienware is a 240Hz Gaming monitor aimed at E-Sports players on PC who want the fastest possible refresh rates. And the Asus you mentioned is a 75Hz budget Gaming monitor, which is a very decent monitor for you average gaming PC/Console.
Hope this helps