GPS or SS

OK as im going off out into the big blue wobblie alot of poeple are talking about having a GPS to track your location or to find reefs.....but ive not hear anyone say your out in open water going to reef where sharks ARE going to be there buy a SS......ive been looking on the net and the GPS unit ive seen that i like is the eTrex Vista Cx around $550 and the SS Freedom 4 is around $700. What would you be spending your money on and why?