We don't really have much idea about how the Roman subarmalis was constructed. If it looks a little like one of the Roman depictions of this garment and makes your armour fit more comfortably then it is probably a good one to buy. The one in that photo looks way too long. The ptyruges should cover from your lower stomach to the top of your thighs.
That's the Deepeeka one I think.
This Subarmalis is horrible.
Even from practical point of view, leather torso is close to being useless vs linen-cotton-linen construction.