Materia Transmutation

I am pretty new to this concept and I looked on google but I am only finding bland answers. I understand you can trade in 5 materia and get 1 back.

My questions revolve around upgrading materia types. If I put in 5 level 1 strength materia, am I going to get a level 2 strength materia back, or a level 1 intelligence/cp/acc/ect...

Also.. if I put in 5 level 3 materia, is there any chance I am going to get back a level 2 or 1 materia? Is there any sort of control here or is it a complete gamble? I have tons of level 1 and 2 materia piled up and I am unsure if I should transmute it all for higher stuff, or just sell it on the boards.

Materia only goes up 1 tier extremely rarely.
You put any 5 materia in, you get 1 out randomly of equal or higher value, of the lowest valued one put in.
IE if you put in 1xII and 4xIV you are very likely going to get a II materia as the pay out.

There is no control to it. Even the characters say they have no idea what you will get. Completely RNG for what you get. I'd only use the elemental resistance materias for it since I don't use them on my gear.

Sounds like that system could use a rework. It would be much better if it had designated outcomes, with a small % chance of course. Also if you placed the same type in, you should receive the same in return. Example:

5x Strength I > 80% chance of getting Strength II or 20% chance of getting Strength I plus a Allagan piece.

5x Random Materia I > 80% chance of getting Random Materia II or 20% chance of getting Random Materia I plus an Allagan piece.

And then with each additional tier the % chance of increasing in level would go down 10% or so.

I > II = 80%
II > III = 70%
III > IV = 60%
IV > V = 50%
V > VI = 40%

However the Allagan Piece you get for each failed level would also increase making the blow not as bad. Tin, Bronze, Silver, Gold, Ect...