I always use the Delta app on my phone. Put the boarding pass in the wallet and use that for boarding.
The Delta app on my watch gives me notifications about flight delays, gate changes, and updates like "Your bag has been loaded on the plane".
In the beginning I sometimes had a problem with the boarding pass not registering on the scanner, either at the TSA checkpoint or the boarding gate. But I figured out that it was because my screen brightness wasn't set high enough. That's easy to fix with a quick swipe in the control panel, and I've never had trouble with it since.