The GWS has one benefit - the price. Its only got a max movement of about 90º, so I had to compensate with a longer arm than the standard one that came with the boat. The sail movement is also enlarged by anchoring a sheet at the stern, then forward to a pulley attached to the servo arm, back to the stern again where runs over another pulley and finally forward. The sheet is then divided in two: the first goes to the main sail and the second to the foresail.
One thing to make sure of is that your sail servo is very firmly fixed in the boat. The force of the sails will otherwise pull it out.