Materia

[Naberrie]

They would see it, and if they're conscientious at all would tell you there's an alert. But the only way to be 100% sure is to do it yourself.

This is how I started doing it. First, I looked at what stats were already in the piece and ignored those for materia. If it had STR, I'm not going to bother trying to add more STR. If it had ACC, I'm not going to bother with ACC. You will usually get an alert when trying to add the same stat to a piece that already has that stat. Particularly if you're dealing with HQ gear.

The next thing I'd do is start with a higher grade materia. If it's a low level piece, I'd try a grade 2, and see what alert I got. If I didn't like what I saw, I'd back out and try a lower grade to see what happened. It will tell you before you attach the materia how much of the materia will actually attach.

After you've done it several times you'll get a feel for it, and will be able to tell before you even start the process whether it's going to work, based on the gear's level and the stats already on the piece.

[Niwashi]

First, I looked at what stats were already in the piece and ignored those for materia. If it had STR, I'm not going to bother trying to add more STR. If it had ACC, I'm not going to bother with ACC. You will usually get an alert when trying to add the same stat to a piece that already has that stat. Particularly if you're dealing with HQ gear.

This isn't always the case. For instance, when I first unlocked materia melding, I tried it out on the HQ Cotton Chausses I was wearing at the time. Since they already had Control +13 boost without materia, I figured I probably couldn't add any more Control but would be able to add other stats like Craftsmanship. Nope. It turns out I could not add a tier 1 Craftsman's Competence Materia (Craftsmanship +3), but could add a tier 1 Craftsman's Command Materia (Control +1). So the "avoid already-present stats" rule didn't apply there.