In Wingstabi Easy Mode you can only change the servo speed globally, whereas in the classic firmware you can change it for individual servos.
But digital servos will still work fine on the analogue setting, the faster speed just means they can respond quicker to correct model movement. If you were flying a responsive 3D model then this may help in prop hanging but for an Easy Glider you wouldn't notice, the digital servos will provide the same torque regardless of the update frequency. Note you can't use analogue servos with a faster refresh speed or they may overheat.