What is apt-fast and should I use it?

It appears to use the program axel to download the files using multiple concurrent connections to multiple mirrors. My guess is that everyone isn't using it because most people don't have connections that are significantly faster than the mirrors, and therefore, can substantially benefit from concurrent downloads, combined with the fact that most people haven't heard of it. This is the first time I've ever heard it mentioned in 5 years of running Ubuntu.

apt-fast is a shell script wrapper for apt-get and aptitude that can drastically improve APT download times by downloading packages with multiple connections per package. Apt-Fast uses the Axel download accelerator in Ubuntu 12.04 or the aria2 download accelerator in Ubuntu 14.04 and beyond to download different pieces of a package simultaneously, lowering the total time it takes to download a package.

The apt-fast package can be installed in all currently supported versions of Ubuntu by adding the apt-fast/stable PPA to your software sources and installing it using these commands.

sudo add-apt-repository ppa:apt-fast/stable 
sudo apt-get update
sudo apt-get install apt-fast  

During the apt-fast installation process, you will be prompted to perform some package configuration. After successfully installing apt-fast, simply use it the same way you run apt or apt-get.