The MRC adapter works fine within the MRC ecosystem. It will allow up to 8 connections using a standard apps. WiThrottle for iOS devices available on the Apple Store
Engine Driver for Android devices, available on Google Play. The gotcha is to make sure you don't have a cab address conflict. the default address is cab 2. if you have two devices with the same addresses connected then it get wonky.
The Digitax system has the LN Wi-Fi adapter which allows only for 4 connections. But local net will allow up to 8 adapters for a total of 32 connections. I have implemented the Digitrax adapter in my system and at the club. We have one of our OP-Sig members with the MRC advanced system with the MRC adapter. Out side of the address conflict on setting up it works well. We can go over to his layout and use our iPhones to control the trains. The MRC system is not that bad. Their mobile decoders sound/nonsound on the other hand iare another story.
WIThrottle and Engine driver can also be used with JRMI but it now requires the use of a PC and adapters to your DCC system. The cats meow system of the day is the ESU WI-FI system but it will lock you into ECU's ecosystem that works great with ESU products and so-so with others. The Digitrax, MRC, and NCE systems work well with all brands of decoders.