Not so much the two stage acceleration, but the Geo Soft Touch kit (upgrade for the Geo, stock in the Geo+ and incorporated in to the Geo2 bolt kit), among several advantages, slowed the bolt acceleration, making the marker handle fragile paint better.
With regards to the Ego, newer models with the Zick rammer as standard, or those that can accept it as an upgrade, do have a two stage rammer/bolt acceleration. Most of the air in the rammer cap is expelled when the rammer reaches the end of it's movement. The o-ring around the inside of the rammer seals against the Zick extension of the rammer. As the rammer accelerates forwards, this seal creates some degree of vacuum, which tries to pull the rammer back, slowing it down. Once the Zick extension moves passed the rammer cap, the vacuum is broken, and the rammer and bolt are free to accelerate unrestricted. So you have an initial slow acceleration, then after the rammer and bolt have moved forwards a short distance, they can accelerate freely.