Hey there,
To answer your question on the MIDI Maestro, it has 3 modes: The 2 preset default modes for the Aeros and the BeatBuddy and the optional Custom Mode. The custom mode can be edited to handle all sorts of MIDI Commands, you can read more about it in the MIDI Maestro Manual.
Make sure your MIDI Maestro firmware is up to date on version 1.1.9 and that you have the MIDI Maestro app (Google Play Store/App Store)downloaded.
You can control both the Aeros and BeatBuddy, or any other MIDI-capable device, using the custom mode. You can create the custom mode using the MIDI Maestro app. Check out this thorough how-to video on how to use the different MIDI Maestro app functions to customize your mode:
There are no downsides this is a very common use case and I, personally, use it this way all the time 
If you are using Onsong or any iPad controller, you’re going to like that the MIDI Maestro can be easily used as a BLE to MIDI converter. Simply connect your control app to the MM while it is in BLE pairing mode (hold the Bluetooth button on the back of the MIDI Maestro for 3s until the blue light is blinking) and it will convert BLE into MIDI. This removes the need for a BLE dongle to be used.
Thanks for the question, hope this was helpful, let me know!