Never done either... but my reccomendation is to bring your detector to both. The 3 times i've been to Grand Cayman (and 1 trip to Cayman Brac) were all before I started detecting. However, I do remember being @ the Hyatt on Grand Cayman and watching a very attractive woman in a very tiny bikini (ahhh the memories....) get swamped by a wave and come up missing just about ALL of her jewelry. Rings and hoop earrings got swept right off.
definitely take the detector
steve