@shinokada, The differences are that one option is for adding tasks for gem maintenance (bundler-tasks) and the other is bundler support to your project (bundler).
--bundler-tasks adds the bundler gem tasks for gem maintenance tasks (like build, install, and release. Template.
--bundler adds bundler to your project as a dependency, a Gemfile, and some information to the .gitignore. Template.
I am wondering what differences are between using --bundler-tasks and --bundler.
Thanks for your hard work.