CodeIgniter has a small footprint, just 3MB and that's including the user guide.

CI4 will be out soon & is a rewrite..
"CodeIgniter 4 is a rewrite of the framework and is not backwards compatible."
So it will support ALOT more newer functionality built-in.

Setting up CodeIgniter is quick and easy. You can download the version you want from the CI homepage or directly pull the latest version from GitHub. After that, you unzip the contents to the directory that's required. The final step is to edit the config.php to suit your needs and it's set up and ready for development.

There are also a lot of guides and tutorials from developers who have been using CI for a long time. This is because of the relative old age of the framework and the large community behind it.

CodeIgniter is tested by hundreds of thousand of developers that use it in production. This means that it's very hard for any bugs or problems to go unnoticed. Even when a new version is out, bugs are quickly found and patched up.