The door needs less counter weight as it goes up. In order for weights to work you either need several weights, with different weights bottoming out as the door rises. Or have the cable on a spiral pulley may work.
The counter weight is always taking the full weight of the door, there's just a linkage which rotates the door on the way up. So, not the same as the spring ones, which follow a curved channel.
This makes me less keen on them as in theory it's going to fall when it wears out, albeit with only 50% of the weight. Unless there's another failsafe.
Thinking about it, the failsafe should be that if one side fails first, it gets stuck against the track. Although I don't think the one in the vid would, because the track points inward
Ok I've found a video with one in: https://m.youtube.com/shorts/zLuJYlHBSkU
The counter weight is always taking the full weight of the door, there's just a linkage which rotates the door on the way up. So, not the same as the spring ones, which follow a curved channel.
This makes me less keen on them as in theory it's going to fall when it wears out, albeit with only 50% of the weight. Unless there's another failsafe.