The short version
Both are red light masks described as FDA-cleared (Omnilux: 510(k) K191629; Dr. Dennis Gross: per the brand). Omnilux is the flexible-silicone comfort reference. Dr. Dennis Gross is the hard-shell dermatology-brand dual-spectrum alternative.
When is Omnilux Contour Face the right pick?
If you want flexible-silicone comfort and red + near-infrared coverage for anti-aging — Omnilux is the right shape at lower price.
When is Dr. Dennis Gross SpectraLite the right pick?
If you want dermatology-brand pedigree with dual red + blue spectrum (anti-aging + acne) and accept hard-shell comfort trade — Dr. Dennis Gross is the right shape. Shortest session time in category.