The Prizm will work fine on the dry sand, but could get unstable near the wet or saltwater. I assume you mean a saltwater beach. The ground balance would have little effect on being able to be hunting in the wet sand due to the conductivity of the wet salt and black sand in the area. Turning down the Sens. would help there.
Having a detector that ground balances will get you a little more depth in some areas. But also having it set wrong will not help. I don't trust the detectors that "auto ground balance." Fisher used to advertise theirs as being auto when in fact they were preset. I'd rather do it myself so I know it's working.