I'm the maintainer of Rails Composer so I believe I can answer this question with authority.

I respect (and share) the urge to build from scratch. That's a healthy impulse. Rails includes a facility for application templates (Rails Composer is an application template) because automation saves time and effort. For people who build many web apps, a time comes when you decide to automate the process.

Rails Composer offers an advantage over roll-your-own application templates because it is open source, used by thousands of developers with code contributions by many. As Rails and gems change, Rails Composer gets updated so you get a current "reference implementation" every time. It gives you well-tested starter apps that integrate all the bits and pieces that require tweaking, like RSpec plus Capybara and FactoryGirl, flash messages and navigation with either Bootstrap or Foundation front-end frameworks, Devise or OmniAuth for authentication, Pundit for authorization, and many utility gems that developers like to add (Guard, Pry, etc.). It lets you choose your stack (for example, ERB, Haml, or Slim), offering choices to the extent that the community has contributed options.

If you're concerned about the safety of running an install script, the code is open source and used by thousands of Rails developers (you can see over 2000 watchers on the GitHub repo). It's purely an application template using the Thor library, and though in theory someone could contribute code that tampered with your files, we'd never accept a pull request like that. Rails Composer only offers well-known popular gems, so you are not exposed to potential risk of using unknown gems.

Rails Composer is widely used, particularly by consultants who build lots of apps. Many of the prominent consulting firms have an in-house application template (Thoughbot Suspenders, for example) and some use Rails Composer or the rails_apps_composer gem that generates custom application templates. Developers who work on on only one application regularly (maintaining a big project, for example) tend to be less familiar with application templates like Rails Composer, but it is popular with developers who start a lot of apps.

Stack Overflow is not a place for opinions, so if you want a range of opinions or debate about the merits of Rails application templates, Reddit or Quora might be a better place to ask.

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