Rails 5 Use Bootstrap CDN without gem
<p>I'm starting a Rails 5 application with Bootstrap 3, I'm confused whether to go with gems like <a href="https://github.com/seyhunak/twitter-bootstrap-rails" rel="nofollow">Bootstrap-Sass</a> or use CDN from MaxCDN to rails application.css/js file. I don't plan to modify bootstrap styles, is there any added benefit in using gems other than modifying/mixin. </p>

<p>Using CDN versions should perform better than of gem ?
If I use CDN method there is added benefit of not loading styles/script if user already has it locally in browser ? 
Is there any cons for using CDN links in Rails ?</p>