I've checked and used it myself it's very simple just start the game load your save, use the trainer and press access TLR.
You can add items, set Max unions, Max Battle units, Max units, Battle Rank, Chains, Items.... Pretty much anything can be changed with it simply and while the game is running for instant effects.
Read the read me for more information but do not make Battle Rank negative or a number way to high or the game will crash and your save can be corrupted keep it at 0-150 to be safe feel free to try higher just be careful game can auto correct if value is strange but as I said high chance for corrupt save.
PS: The best part in my book is probably the fact that you can add any skill to any character meaning you can make a team with who ever you want and make them any kind of unit!