The folks I camp and offroad with have not been all that happy with their rooftop tents.  Here is what they have said.
- The tent and vehicle are tied together.  All too often, we get into camp and get set up, and then decide to take a drive.  That means taking down the tent and delaying the group. 
- The tent up top is really cold in the winter due to air being on all sides. 
- The tent up top is a crawling around affair making it tough to change clothes, etc. 
- The vehicle rocks every time one of the roof top tent occupants moves or rolls around. 
- The tent on top puts a fair amount of weight up high thereby raising the center of gravity of the rig. 
- The tent on top kills fuel mileage. 
The folks I camp and offroad with have found these solutions work better:
- A conventional, ground-based tent is a great alternative to the rooftop tent.  Preferred brands include the made in the USA Springbar tent.  Once camp is established, you can take a drive and not have to break down the tent. 
- Conventional tents are much warmer in the winter due to not having air underneath. 
- Conventional tents like the Springbar allow the user to stand up and stretch out. 
- A tent on solid ground does not move around when users move around. 
- Conventional tents don't raise the center of gravity of the vehicle. 
- Convention tents don't impact fuel mileage.