With the BlueRailTrains app, I have worked out a procedure which allows two separate smart devices to independently control two BlueRail equipped engines at the same time. Am not sure if this would work with EZ-APP.
App based operation of model trains is definitely here to stay and is a serious wave of the future. One issue which is pointed out in this thread is that apps seem to work better with IoS than with Android. I currently run transformer based conventional, hand held controller (LC & TMCC) and app based Once you get used to app based, it's really convenient to use and has the advantage of continuous feedback display of operating conditions.
You can install the BlueRail board which is the heart of the Bachmann EZ-APP. I have done this successfully on eight OGauge locos and they all work well. The BlueRail website has details for this conversion.
These were taken the first day. I purchased the bluetooth circuit boards from BlueRailTrains who makes the boards for Bachmann and switched them out with the E-units. The BlueRail boards work very well controlling my OGauge locos. You can see videos of this on BlueRail's website (www.bluerailtrains.com).