CI v2.1.2 to v3.1.5 Upgrade Problems

The guide to upgrading is here:

https://www.codeigniter.com/user_guide/i...e_300.html

Have a read through and see if the developer's concerns match the upgrade issues listed.  I would, honestly, devote a small project to just doing what the update suggests and then seeing where you're at for problems in the site (clone the code base and branch off to an "upgrade" project so your existing code isn't touched) - the concerns may be justified or it may turn out to be a less problematic update.  Having done a v2 to v3 update on a huge custom project, we didn't spend more than a month on it (really trying to remember if I even spent more than a week on it) - and we have a significant amount of legacy, non-CI, code mixed in with CI.  The most annoying thing was the Ucase on the class names....