Hello James!
Short answer is yes you can install CodeMix in your MyEclipse installation and you will get the same features you would get in Angular IDE.
In this case you did right on choosing CodeMix instead of “CodeMix Enterprise” in the Marketplace, but then you need to select to install only “CodeMix Essentials” when offered in the “Confirm Selected Features” Page.
We are working on making this more clear at the moment of installing on top of MyEclipse, Sorry for the inconvenencies.
Cheers!
Aaron Lara