A major selling point of the RG Mechanics repack is the inclusion of the full Tyranny of King Washington DLC. This is a "what if" scenario where Connor never became an Assassin, and Washington uses a magical apple of Eden to become a dictator.
If you want to experience the journey of Connor Kenway safely and legally, the best option is to purchase Assassin's Creed III Remastered on Steam or the Ubisoft Store. The Remastered edition includes higher resolution support, improved UI, all DLCs, and native support for modern operating systems without any of the security risks associated with scene repacks. Assassin's Creed® III Remastered on Steam Assassins-Creed-III-RePack-RG-Mechanics