+1 on the hard- vs softtop roof top tents.
I've used a mates RTT for a few weeks, that was nice. So now me and my mates have a few Chinolina's and am impressed by the quality.
It's on my roof for more than a year and a half now, gets a lot of abuse from branches in the forest, I load it up with wood, steel etc and it holds up fine.
The hard top models are really easy to set up and take down, I've got a triangle hard top model myself (140*215cm / 55*85inches).
I'm 188cm / 6'2 and can sleep with another person comfortably inside the RTT. Perfect for a la 100's in the hills.
I always have my sleeping gear in the tent, when I go to bed I get the ladder, undo the latch and it pops up.
In the morning I go out, eat some breakfast, close the tent and am om my way.
The speed of setting up (30 secs including getting ladder) and closing it again does it for me. It's also nice to have a comfortable matress to sleep on.
It is also possible to open up some ventilation, inserting the steel pins takes some more time but not more than a minute.
I've also used a softtop / folding tent but that one did take some time to set up. I also had to take the bedding out, did not like that, was a little bit more spacious though.
Before I had the roof top tent I used a pop up tent, that was also fine but you could only set up on relatively flat ground. With the roof tent I can go on rocks, gravel and wet places without a problem. I just make sure I'm relatively level, if that is hard then just point the rear (where my head is) a bit up and it's ok (it does not have to be perfect).
I'm 25 and I have no problem with the ladder. That said I was on a trip in Albania last year and spend a few days camping with a couple in a Maggiolina (wind up) roof top tent on their LandRover Defender. That vehicle is quite high and they had no trouble at all getting up their (fancy)ladder (age around 65).
The downside is the thing on your roof, it's kind of bulky, caches wind and makes some noise. You'll probably notice it when cornering too. Another downside is that you gain height, I use my HDJ100 as a daily driver with the RTT on it, I can't fit in parking garages anymore. Also when offroading in the forest sometimes I have to be careful with trees while leaning the vehicle to one side. Other than those things I do not see any downsides.