As probably one of the few people on here who has had one, I can fill in a few details.
If you are looking at the largest one, the one I had, it is really heavy. It took 4 of us to move from one vehicle to another.
It has an amazing amount of room in it for a hard shell. The largest one available that I am aware of.
Set up time is fairly quick. Probably 3 to 5 min, even quicker once you get used to it. Tear down is a pain in the ass for one person. It is very difficult to pull down the front as the struts are pretty strong.
Completely securing it for travel can easily take 10 to 15 min for one person to get everything tucked in and buckled down correctly. (mine was the original demo model so they may have improved some of the issues)
The straps are a very weak point in my opinion. There is a lot of stress on those rubber straps and they are not very thick. But I never had a problem with them in my 5000 mile trip.
It has pretty decent aero-dynamics as far as roof top tents go. My average mileage around town and on trips was 15-16mpg without the tent. On my 5000 mile trip with the tent, I averaged 18. Maybe I got lucky with the winds or just driving slower enjoying the scenery but it is what it is.
I didn't really notice it up there until I went around corners a little too fast. You will quickly notice the extra weight up top and will adjust your driving style. This will be the same with any large heavy load on top of a lifted vehicle.
It is pretty comfortable and spacious inside. Since it was just me, I didn't deploy the shelf and had a double thick mattress. I think the thinner mattress might be too thin for a larger person.
The plastic windows are a pain in the butt. But it is nice to have them if it is windy or rainy but you still want to see out.
It has really thick material and will keep you warm in most weather conditions. Might be pretty toasty in extreme heat but my trip was around the PNW in late June/early July and I really didn't have any issues.
I ran a USB cable from the 4runner to a hub in the tent and hooked up a USB fan which worked really well. I have a couple of magnetic pool lights that have a remote which I used for lighting.
There are some pics in my build thread here
http://www.toyota-4runner.org/5th-gen-t4rs/207663-tiggers-build-mis-adventures-7.html#post2395449