RE: appropriate kedge anchor
I've not heard the term "kedge" anchor applied to an actual anchor type. Kedging is the process of taking an anchor out in a ship's boat (or your dinghy), dropping it some distance from the parent ship or boat, and then setting and pulling against this anchor to haul the main vessel off the bottom. Any anchor that will set and hold in the bottom type will work as a "kedge anchor." At least that 's the way I understand it.
A Fortress sized to be the main anchor for your boat would be a good choice for light weight and holding power....IF..... the bottoms you boat over are conducive to using a Danforth-type anchor. If you anchor in sand or mud a Fortress would be ideal. If you anchor over rocky bottoms or weedy bottoms I don't think a Fortress would be the best choice.
Our yacht club has cruises to a few locations during the year when we raft up to 15 boats (or more). In addition to bow anchors being deployed by every fourth or fifth boat, we also put out some stern anchors and some anchors angled off from either end of the raft. The anchors that are used for the stern and "angled" anchors are regular anchors. We "donate" our Fortress and stern rode for use as one of the angled-off anchors. I've not heard the term "kedge" used for this function, but perhaps that is another use for the term.
The grapple-type anchors are good for dinghies and perhaps for "normal" boats in extremely rocky bottoms where they will snag and hold against boulders or whatever on the bottom. But I can't see them holding any substantial weight in sand, mud, gravel, etc.