Normally it's advertised with signs. However, the weather was definitely going to be bad on our sailing, so I didn't see any notice.
In the past, the break even point was ~4 cocktails or 5 beers. That's hard to do if you are there from 8-2. If you have a long day there, it's a decent value - but only if you are committed to drinking on the beach. I honestly don't think we got the HMC beverages in close to 20 years. We're good for a drink or two on the island, but that's about it.