I find GDMSS plus much more user friendly than the BI app. I generally configure both up and switch between the 2. I configured the same setup for a few friends and family and they all also preferred the gdmss plus app. If you have your firewall rules right you can just set both up and switch between the 2.
The suggestion about using UI3 on mobile is just a pain! you want quick access, mobile push alerts etc not open a browser, open a new tab, find/type your bi url/ (or favorites > BI url), wait for it to (auto) log in and load up etc... and then it looks AWFUL on a small mobile screen I want quick access - 1 button push and i'm in. i.e. Gdmss - click the app icon and its straight into live view with my configured favourite - done.
BI mobile app really does need a lot of work to make it nicer, consider its £10 and gdmss is free (and better in my opinion).