These springs are cheaper than most available, so I was initially sceptical that they might be of inferior quality. They bear the CD (continental direct) name though which is reassuring. The spring dimensions differ a little from the GM originals, but they fit OK and the car ride height is unchanged. The springs possibly seem a little stiffer when driving, but this may just be that the originals had weakened and one had broken. I can't comment on how long these springs will last as they've only been on the car for a couple of weeks, but I can't see any reason why this shouldn't be as good as the originals (100,000 miles).
I'v only just bought the front and rear coil springs in April of 2020. The price of the coil springs are a reasonable but low price compared to other places. The quality of the coil springs is yet to be seen but from my inspection and view of the springs they look to be good quality coil springs.