The AROSPEED engine dampers are not pneumatic nor hydraulic.
They have sort of a PU bush inside the cylinder acting as dampeners.
Over long period, the bush will wear.
I''m using AROSPEED engine damper for about a year now, so far its still quite firm.
BTW, each kit comes with 2 bush. A HARD and a SOFT bush.
Frankly speaking, during hard driving I could not feel much difference with the dampeners installed.
But during engine dyno, the engine flex was very much reduced.
WHen the engine was dynoed without dampener, the engine look as if it was gonna rip itself out of the chasis mounts.