We've had an Admin mod for a while now, before they created an app for it. With ours it is not device specific. It is a mobile skin that runs on your X-cart back end. You're welcome to check it out and check out the demo:
http://www.bcsengineering.com/store/mobile-admin-app-for-x-cart.html
We've converted most commonly used admin pages to responsive, if you see a page that's not responsive you are welcome to request it and we can see if it makes sense to include it in the module.
thanks,
Carrie