The main requirements for a tool to help the handling of muti-repos are:
Platform independent: it must support Linux, Windows, and macOS
Solve the issue of commit dependencies across git repositories, especially in the context of CI
Efficient: the tool should minimize the time needed for getting the source since it can be a sizeable percentage of the time spent by a CI engine
Fast execution: the time spent to run a CI is precious
Have a certain level of compatibility with existing tools solving similar issues, i.e., Google repo tool
Has own manifest format for supporting new functionalities but supports conversion from and towards other manifest formats
Built as a library to allow scripting extension, easy inclusion in other tools
Built as a modular SW, not created as a single executable
Decent amount of unit tests
Self-contained: not relying on and using other command-line tools, i.e., git