Thule works okay. You need 3 items: 1: a pair of bars, 2: the appropriate 'feet' and 3: the rubbers, grommets and bolds to connect it to the car. Look closely what you need. When changing cars, it's often only #3 that you need or #2 and 3.
Box: I have one that opens at the back. Safe when you drive: it cannot flip open at the front; the hinges are there. But when you have a long (stretched) car, it can be a pain to get behind the vehicle and reach for the lock of the box that's somewhere halfway above the roof. In that case, I would opt for a box that opens at the side. Make sure its lock sits at the 'safe side': not that you're on the hard shoulder of the motorway between your car and passing cars!!!
Modern cars often have fixed positions where to attach the bars: you can only install them on the car with a pre-set distance apart. Check if the box you're after has the same positions (or is adjustable) when you want to install the u-bolts around the bars and onto the box. Older boxes have holes that are further apart. Eg. I was unable to install my 10 y/o Thule box on the roof of my VW Up! the position of the bars and the holes in the bottom of the box didn't line up.