Most new model cars come with isofix automatically. If not you can have then fitted to your car, pretty cheap, but I'm sure qashqai would have them as its a family car. Not exactly sure what you are asking but they are clips that connect to the chassis of the car and you clip the baby seat directly onto them, therefore much safer in an accident as you know baby seat won't go anywhere!
Most seats now come with isofix clips, maxi cosi included. Personally I find them much easier, you just clip the seat straight in takes a few seconds as opposed to fiddling with belts. You don't have to have them, I think most seats do have the option to use belts as well but check when you buy them.
Isofix were introduced as they are supposed to be much safer. You don't have to rely on a belt to hold the car seat in an accident and it stops the seat being improperly fitted ad the belt slipping off. Personally I would recommend them, for ease if nothing else but it is totally down to you, just make sure they show you the proper way to fit the seat with a belt.