Update - we went out Sunday and while fairly calm the new stern anchor worked fairly well. There were a couple things I could have done better but overall it served its purpose.
If it does not dig in , it has the same holding power as a cement block of the same weight.I finally made my trip this year to Toronto Island. I initially tied up at the mooring wall but on the second day, I anchored out by the beach. I used the navy anchor off the bow and the small fluke off the stern. The stern line was at a 45 degree angle. The wind picked up a little bit to 10kts with very minor chop. Most of the boats swayed with the wind. After several hours I looked at the stern line and noticed it was now 90 degrees off the stern. Hmmm, how could that be? I jumped in the water and swam over to the navy anchor and could clearly see that even though the chain was flat on the surfaced and the anchor is dug in, it got dragged around 7 feet or so. Its a sandy bottom but the navy anchor didn't seem long enough to dig in far enough. So I repositioned it and it remained steady from there as the winds reduced. With all that weight, it surprised me.