Salman, the ATS SS II is preferable to the X-2, IMO. They are very similar, but they have changed the tension head stand and it is now a stamped part held together with bolts where as the SS II's is a 1 piece, cast part. A clutch or ratcheting tension head allows one to raise the drop weight arm while holding the rotating head stationary. Without this the drum and the arm both turn and you have to either release the string from the drum or let it slip to give it more slack if a second pull is needed. Most people feel it is easier to string on a drop weight machine that has a clutch.