I have an Arsenal on pre-order. First, it most certainly does support iOS.
I agree that it is in no way a necessity. The things I am most interested to try with it is the software ND (SmoothReflections on my A7R ii) and focus stacking (which I don't know much about.) I believe it will also use your phone's GPS for geotagging, which my A7R ii doesn't do but my 5D4 does. Lastly it will give me a way to do focus peaking on my Canon. I guess I'm a sucker, but I am excited to see how this thing works. I think it has a lot of promise.
I will certainly come back and post my thoughts once I receive it in April/May.