Hello,
I have access to both systems (last year upgraded my 5E to 5.5 Entry Audio 20 - Code 506) and another W213 with factory build in NTG 5.5 High Command.
Both systems provide support for Car Play and Android Auto, both have 12 inch screens and to be honest, if you switch to Car Play they behave identical e.g. nearly the same speed, reaction time to commands etc.
The 5.5 Entry navigation is not so slow as my previous 5E Head unit was. It runs from SD card that can be easy exchanged with updated map version.
Command navigation runs from hard disc build in the head unit. Maps update is also very easy over the USB stick and Mercedes Download Manager software. (you need to buy access pin for map activation).
In general both navigations screens looks very similar and the usage too. But I didn't compared all the functions very deeply.
Regarding the sound quality: I upgraded my front speakers and additionally the bass (from 16cm to 20cm) and I believe that the sound is much better than in the car with NTG5.5 High (Command). Much clearer and more punchy bass, better high frequencies.
In USA Command provides Sirius (Satellite) radio, and DAB (Digital Audio Broadcast) is also possible.
If you don't have CarPlay/Android Auto support in your NTG 5.5 Entry then first try to activate it and check whether maybe those functions are sufficient for your needs before you upgrade to command.
I am not native English speaker, therefore above text can contain grammatical and other errors. Sorry.