I am new to Emacs. When I started using it 2 months ago, a co-worker suggested using helm which definetly improved my use of Emacs.

In addition, I have been slowly reading the book Mastering Emacs, by Mickey Petersen. At the beginning of the book, the author emphatically endorses using ido-mode. So, I installed it and I have been using it for the last 2 weeks. Since I have not uninstalled helm, I have been using both packages ido-modeand helm simultaneously.

1 - Is there a feature/functionality overlap between those packages? What is it? Or are they perfectly complementary?

2 - Aside from subjective opinions, is there any technical reason to make this a bad "design" choice for one's configuration?

Thanks