Had a good email exchange with David from dev-core. I actually paid the $4.99 for the Mix Station Pro edition.
1. Because I want the additional features and even the ones not implmented yet but when they become available.
2. Give some support to David so he can continue to develop this app for the Android.
Here was his response to me when I asked about the "Pro" version and thought I'd share it with the rest of you who may not have it.
From David:
A full list can be found here:
https://bugs.dev-core.org/w/ms/xair/pro_free/
Note that not all pro features are implemented yet but in the end all the features listed there should be available.