The Lite rules actually give you the game rules for everything except undead, cannon, and maybe the solo rules.
The full books give you the rules with "history", scenarios and scenario seeds, special characters, illustrations etc, and are a fun read as well.
So if you fancy taking an elf section against some werewolves, or orcs the Lite rules will give you all you need.
If you like the game having played it then getting one or all of the books is the next step.
Alternately if you have one of the books, give your friends the Lite version to read before a game and you will all be on the same page so to speak.
Bob
PS: Oh, are they any good? Horses for courses but I like them.
PPS: The Black Powder Fantasy board was set up largely to give Flintloque and Slaughterloo a place that was neither Napoleonics nor Fantasy. Posting to that board should in theory give you more focussed…er..actually I have no idea why there are so many sub boards but I can say that if someone is only looking at that board they should have information to share and might miss it if not also reading the Fantasy board.