Hi brannen,
Some of my thoughts about Diamond Mattress are in this thread. As a wholesale manufacturer they are certainly doing many things right and their site is very transparent.
Tri-Zone is a type of zoning where the middle third of the mattress support layers (and sometimes other layers as well) are firmer (to better hold up the heavier hip area and promote better spinal alignment) and the head and foot zones are a little softer. It can certainly have value for people who carry more weight area and tend to sink in too deeply and don’t have enough support there with other types of construction.
Phoenix