Probably just about as much information as most would want on beach plums...
Cornell beach plum write-up
A couple notes on the variability of the fruit:
"The beach plum is extremely variable, as the American Agriculturist observed in its November 1872 issue: “The fruit varies in different plants, not only in color and size, but in quality-some specimens being quite pleasant to the taste, and others harsh and acerb.” "
"The edible fruit, which ripens from late August through September (8, 4), ranges in size from a half an inch to an inch in diameter. The fruit color can be red, purple, deep blue, and, rarely, yellow. The plum has a tart acidic flesh."
Hopefully the ones I have planted will prove to be tasty. I guess that is the fun/risk of planting a wild plant.