I've tried LED masks for firmness before and didn't see much change. What makes this different?

Most LED devices lose the majority of their power before it reaches the cells that matter - up to 95% of LED light bounces straight off the surface of the skin. Laser light behaves differently. Because it is coherent, polarized and monochromatic, it creates what is known as the Speckle Effect, amplifying the light's intensity through the full depth of penetration rather than scattering at the surface.

That is the structural reason LED can warm the skin without meaningfully rebuilding it, while a true laser reaches the fibroblasts that produce collagen and elastin - the two proteins responsible for turning loose, saggy skin firmer again. You can read more on the difference between LED and laser light therapy.