ok I am running re-motored brick actuators with 12v motors and jrkshttp://www.youtube.com/watch?v=DXUR-kTz6YY
now on a framehttp://www.youtube.com/watch?v=sI5A9QU9GWw
and they are more responsive and finer in motion, but still harsh.
Then again the motors are definitely smoother, but with good vibration. Very good motors, I use multiturns on them.
The springs didnt really help with these motors, so I eventually took them off.
Cost effective, if you can afford scn5, buy them, if you want more weight moved and with very good motion, use motors.
As said, Bobbuilt is working with these motors, he will more than likely get better results in motion than me.