Yes, I've got a hannibal roof tent had it for about 15 years. Unless you are going on expedition to Africa, moving on everyday don't bother.
They look very gucci and rough and ready. But you if you need to leave your campsite in your vehicle you have to pack your tent away and carry it round with you all the time. Even when you are not camping, using up fuel through drag and possibly rotting up there. Also very attractive to people with sticky fingers who like other people's nice things.
If you do get one, mine folds out over the bonnet and attaches to an A bar on the front bumper,this allows consistent height of the ladder and also allows the vehicle to be moved in emergencies or to level the tent. Most now just have a ladder to the ground which affects on soft terrain or when adding weight to the vehicle such as getting in tent or vehicle.
Mine originally cost me £500 but are x3 the price now.
For the price of them you could buy an everest or Antarctica expedition tent.
------------- Slowly carrying its home on its back
I saw quite a few of them in Australia. But they have poisonous snakes out there. The ones I've seen on sites in UK have all been on German registered vehicles, and on sites where you can get a bus into the city centre for sight seeing.
Ive always like the idea of these and occasionally actually think of getting one. But reading the post from lescargo reminds me it's that it's probably the idea of them I like rather than the reality.
As a follow on - we were at Mortonhall site recently (Edinburgh) and there were 2 such tents, both Continental, both being used by single mature men & not travelling together. And both very different - one looked like it would go on safari: all canvas, almost a pram top style. It looked like folding it away on your own could be fiddly.
The other looked much smarter & easier - like the pop-top roof of a campervan, solid moulded top matching the bottom like a clam, and sprung side supports. It would pack away in minutes.
Both tents were there at least 4 nights. But there's a bus stop at the gate & loads to see in the city.