Who to use metis's tome on?

Amelia.

I'm say Amelia as well. Especially if she's a general.

Metis' Tome shows no visible addition to the unit you use it on. It increases maturity, and I still haven't figured out what that does. Every time I get it I give it to Ross. He's simply amazing as a level 20 Berserker. He can take out pretty much anything in one hit(Demon King in two if it goes right). So, I'd say Ross, but give it to your favorite unit.

Metis tome raises all Stat-up percentages by 5%.

Anyone that you want it's your choice it doesn't really matter. So just use on your fav character

Im embaressed to ask but what and were do you get Meyis tome?

It's in the desert on Ch. 15 in the top right corner. It's in a 5x4(or 3) square. Take a unit with high Luck up there and just go around in that area til you find it.

Thanks Sir Ronny your very helpful.

Garcia or knoll (if you plan using them)

There is no single best unit to use it on. The character that will gain the most benefit from it is basically the one that will grow the most from the time you use Metis Tome on him/her until the end of the game, which will usually be one of the trainees.

I would say Eirika, She's pre-premotion by that point so shes got a good 20 levels to level up. she kinda sucks stat wise and she's essential.

If you've held off on grinding a trainee sure why not, but that means your likely gonna use the tower... and well plenty of spare stat drop items fall in the tower and Ruins... So its kinda moot to wait that long. and just finish off the unit with stat drop items (Amelia gets +Def items for example, Ross gets +skill items... mages get +HP items etc.)

i say Trainees
since they have more level up than any other units

If you're going to use the tower/ruins much, and want to use one of them, give it to a low level trainee.

It's still all up to chance the stats you get, of course, but I would suggest Amelia, too. She's likely to be somewhat low at this point. She has fairly balanced stats, with high speed. She's one of very few potential generals, and a general with high speed is not only the best tank, but an unstoppable killing machine.

If you're not using trainees, then just go with whoever you've decided to use who's on the low-ish end of the level scale. It's best to give it to a melee unit, to avoid wasting some potential from the defense, skill, speed, and luck.

i know this may be dumb but i used it on Seth same as the boots (don't judge me hes the best i got ever well maybe Duessel and Gilliam are better in some areas but hes fastes and strongest)