Hi @helb, author here. ZSH's tab completion looks awesome! I'm not a ZSH user so I wasn't aware of that but I'm happy something similar exists in that ecosystem.
Re multiple files: I've thought about this a little, but I'm not sure how the UI would best represent the (potentially conflicting) permissions of multiple files. Open to suggestions however! In those situations I personally use remod to remind myself of the proper chmod command, and then copy-paste-run the chmod command with whatever edits are necessary.