Hey Doug,
Be really careful using that rock slot, I just don't see the point of doing so. I'd only consider it in very specific situations, perhaps when anchored in a spot like the Alligator River where hooking a snag or submerged stump might be a possibility, and you wouldn't be leaving the boat. Even so, I'd probably still use a trip line, instead... The one situation where the rock slot might be useful, could be if you were Med-moored in a harbor that might have a lot of debris or old chains/cables on the bottom, and where a trip line could be problematic due to other traffic, etc... But I still view it as a gimmick, and Manson only did it to differentiate the Supreme from the Rocna. It's the thing I like least about my anchor, I wish Manson would just get rid of it...
Good luck, I'm sure you'll be happy with yours... Just keep an eye on your shackle, haven't looked at the newer Mansons lately, but on my older one, the edges of the hole in the shank were not very well finished, and had a rather sharp edge... I'd guess an ordinary galvanized shackle might get torn up a bit, and would have to be replaced every so often... No biggie, but something to keep an eye on...
Glad to hear you're planning to get a long trip to Maine this year, enjoy...
best regards,
Jon