The word "trainer" implies cheating, but in a single-player experience, the only judge is you. Here is a breakdown of when using the FLiNG trainer is justified versus when it ruins the fun.
If you're revisiting the streets of revolutionary Paris and finding the grind for Sync Points or the difficulty of level-5 guards a bit much, the remains a popular community choice. Key Features of the FLiNG Trainer Assassin Creed Unity Trainer Fling