I have the OG habitat I guess. We like the windows for ventilation for dogs. If you don't have dogs I see no reason for the windows.
Habitat vs 4WC. 4WC is a lot more weight and a bigger performance hit. I was honestly disappointed with the interior space of the 4WC. I would look at a Econoline with a 4wd conversion before I would look at a 4WC.
There is a negligible performance hit on an HD Ram with 1200# in the bed, regardless of engine. I see the point of the light weight Habitat if you are in a Tacoma with marginal load capacity and a small engine or if you use the truck for camping every weekend and don't want to reload the popup all the time. Otherwise, the negatives far outweigh any positives.
If you are going to unload everything from the truck bed to use your Habitat as a regular topper during the week, that will take MORE time than dismounting a normal topper and installing the popup if you have access to a forklift as I think Tex does.
The best setup is an 8ft popup camper in the 6.5ft bed. Zero departure angle hit with the tailgate removed and lots of room inside. The end of the camper will protrude about the same or less than a 12.5" wide tire on a bumper mount.