I think the selling point of this mask is just that it hugs the contours of the face and that's probably how you get the firming effect. I tried it once and saw a slight firming only. Unless you are ready to commit to using it frequently, I don't think this might show any huge difference.
Have only tried this mask once, in fact, my first sk-ii mask that I've bought and I have no bad reviews about it. My skin did not feel irritated, and did looked improved.
Don't think its firming at all. The material is very thick and fits the skin quite well, but I find it more hydrating than firming.
This mask really comes in 2 piece, makes it easy to adjust for my face. It is also very moisturizing. As for firming, my cheek did look a little lifted. Might have to use more to verify its effectiveness.