Nope, it’s super interesting. I assumed it was a post-game thing myself, but it’s not.
How it works is this - you make a save game (like you do) and dump out to the title screen. Then you start trial mode, and pick a save game - this is then a snapshot of the characters you are loading into trial mode. So you want to hold off until you are at all 6 characters (and, hint hint, a guest character if you can swing it).
The trial then starts, and your characters exactly as they are in your normal save start kicking ass. You do not gain EXP in trial mode, but you are gaining LP (and a lot of it) from stage to stage as you clear enemies. Also, there are chests, rare enemies, and lots of different things to steal and find in each stage - it’s very deep, not just “kill everything” but rather “kill everything but not before you run around and find that rare hunt and steel a flame shield from it if your lucky” kind of thing.
Okay, so you progress as far as you can. The game makes an auto save at the start of each round, so you can actually retry rounds again (particular useful if you want a chest to have a specific item or to steal something specific from a mob) and every 10 rounds you can make a hard save so you don’t have to start from level 1 every time, unless you want to of course.
So you get as far as you can, which is the fun bit because it means you can periodically take a break from the main game and challenge yourself to get further in trial mode than you did last time, and then eventually you’ll get to a game over screen. No worries, back at the main menu pick Load Game and load the most recent trial mode save and it will actually put you right back where you were before you started trial mode, but with all the items, LP, and etc. you earned during the trial! Or, pick Trial Mode and resume from where you left off, if you wanted to retry.
I guess some folks have been having a lot of luck looting a diamond armband found in stage 1, which sells for 6,000 gil, btw, if your looking for some cash and don’t mind sitting through some loading screens. I haven’t tried it yet myself, but I just may. The encounters are really neat, they are cribbed from the various hunts and boss fights to that point, complete with the same stages and (I’ve read) will feature the same mechanics (such as double-gravity making characters with heavy armor slowed down) as those original fights do.
Once you unlock your second job board, by defeating your first Esper, getting through the first 10 levels in trial mode is a no-brainer, as that same Esper is the 10th level of Trial mode. I noticed running from trial 1 to 10 takes about 10 minutes and yields about 180 or so LP (double that if someone has the “earn double LP” accessory, which I gave to Penelo as she’s my black and red mage). I did this twice this morning just before work, and ended up stealing a Sword of Kings from Belias. It was pretty fucking rad.
Stage 5:
So like I said, a really fun way to challenge your party and in so doing come out with some goodies and lots of LP to help with the fact you have two job boards to spend points on now. I love it, it’s so much more interesting than I had assumed it would be, honestly.