First, please keep in mind that this is coming from a detectorist who hasn't been too thrilled with the Prizm series in general, who has owned a couple of Prizm IV's and has a Coinmaster, and has owned a few Garrett Ace 250's. I am of the opinion that I'd prefer to tackle the beaches, or most any other place, with a model that provides me with some form of ground balance control as well as a wide-range, variable Discrimination. The likes of a modified Classic III SL, IDX Pro, or an M6 or MXT, for example.
A lot will depend upon the GB setting of the detector. I have had less than desired performance on beaches from the Garrett Ace 250's that I had. So, if I had both of those models, I'd anticipate better performance from the Prizm, but I'd take them both and compare them, side-by-side, on the same targets in the same conditions.
I haven't taken the Coinmaster out into the "wet zone" at the beach yet as I prefer better (warmer) beach weather and that will come in a few months. Give them a try and report back to us one YOUR experiences.
Monte