We've just converted to a TT. We find the beds so much more comfy and love the amount of space we get- we have 3 kids and they are only going to get bigger.
Pitching/striking wise it takes about the same as our previous tent but the main advantage is that most of the stuff is in the tent ready to go. So whereas we used to spend at least 2 hours getting stuff from the storage places in the house, fixing the roofbox to the car, carrying it out to the car and then DH almost having a fit to get it all in all we do now is pack clothes, the coolbox and a few other bits and then we go. It's the same when striking.
But there are downsides, I agree about that you might not get as many sites, you do have to level it well (we got a spirit level for the TT), factor in the (possible) costs of buying it, towbars, storage, servicing, insurance, extra fees on toll roads and ferries etc. And it's taken us a while to get used to it, it doesn't quite feel like proper camping yet.