All the PHP frameworks are open sourced that give developers ample of opportunities to make any modification and custom developmnent as per your business requirement.
Content as well as background management is easier in custom PHP as you can get a custom CMS to make those background operations easily
Custom development is costlier than traditional PHP frameworks. However, the additional benefits, custom functionalities you get from here are uncomparable and justify the cost which will eventually seems like cost effective.
Custom PHP supports all servers so it's hassle free to run your website from any server you choose.
Security is the key specification for Codeigniter. Any kind of security breach is not possible. So it's widely trusted by large corporations and developers.