Last winter I had some problems with the brake servo on my Amazon. This brake servo is from a brand called Powertune and it is likely to be made in China. The problem was it wouldn't work after the car had some weeks not being used. By applying a strong foot on the brake pedal it would come loose and work again. This winter this also didn't work: it just stopped working at all.
So I went to my local workshop and the mechanic advised to install a new one. He used a Powertune again, because this unit is much cheaper than a genuine Lockheed. This unit would work but with some flaws. It had a retarded reaction on the foot. After applying the brakes firmly the servo would come in but after a second. Releasing the brake pedal it also released the brakes a second or so later. This is very annoying.
So I got in my car to visit the mechanic again, but now it works much better. Not as smooth as it should be but the retarding is almost gone.