Most folks using smart phones go with the default email application of Android. This is the default GMail application or the standard email application.
The post encourages you to use K-9 Email Client on Android. It is to let you know how you can install a better application that supports more email services and features. With the ability of public email services to read or retain emails to and from your account, you do need an additional level of privacy and on top of it, more email services in just one application.
You can download and install K-9. It is a universal email client. If you need to send or receive encrypted email, then you can install APG (Android Privacy Guard), which is the android equivalent of PGP or Gnu Privacy Guard. Make sure to generate your key pair and send your public key to those with whom you want to communicate securely or place your public key on a key server.
Install and enjoy the convenience of a single good email application and encryption where you need it.