The Dual-Illuminated RMR uses fiber optics and tritium to illuminate the reticle. Fiber optics collect ambient light, automatically adjusting the reticle brightness. In situations with no (or low) light, the tritium illuminates the reticle. This version is popular with shooters who prefer a battery-free solution.
The RM04 family has an amber 7.0 MOA dot, which is simple to use and easy to find. The 7.0 MOA dot is popular for those wanting Trijicon's smallest aiming point in their Dual-Illuminated models.