Virtual reality is best experienced than described. It is a new idea, still far from mass market use. The Oculus Rift’s Dev Kit 1  came only 3/4 years before. 

Why a VR headset for your smartphone? Because  Smartphone VR headsets are an affordable means to try out virtual reality (immersing yourself in virtual space, turning your head, like in the real world, exploring, fighting, and creating) when you want a better option than cardboard viewers but are not ready for fancy, expensive desktop VR sets.

The best mobile virtual reality headset: Google Daydream View (esy to wear, high - end feel, remote to track your hand)

The second best mobile virtual reality headset: Samsung Gear VR (most number of apps, features for serious gamers)

The best affordable mobile virtual reality handset: Mattel View-Master (entry-level VR, for use with  Google’s Cardboard app ecosystem)