Some of the FBs and ARS tubs are either solid colored or solid with "windows" in the front.
So while they drawers don't have siding or backing, they don't need to - the effect of being "enclosed" is still achieved.
Regardless - ARS and FBs are much more expensive. We were comparing AP economy racks and Reptile Basics/Boaphiles.
Some of my younger snakes did not do as well in the Vision rack due to the security issue. With a completely enclosed tub, some of my animals don't even need their hides.
It's not a temperature or a humidity issue. The tub itself holds the humidity and there is sufficient space on the enclosed racking systems that any insulation benefits are probably negligible - at least I've never seen them.
It's a potential security issue for the animals. If you're not backing the racks against a couple of walls, some animals can feel vulnerable in an open sided or backed rack.