why doesn't the devices tap work on the app and why isn't it an option when accessing the router/Gateway from 192.168.12.1

Did you figure this out?  I have the same issue.  I'd like to explore parental controls and network settings, but the web interface has none of that(!) and the app on my phone won't access the Devices tab -- probably just like your issue.  In the reviews of the app it seems like a common problem.  In short, for us at least the service is great, but the configurability is about non-existent.

This is a huge problem as I was needing to be able to turn on and off devices from my phone. With 5 kids, it's an important feature to NOT have working.