Delta is a great anchor, as is the Spade, but I have found when observing the anchor while snorkeling that when the bottom is very hard packed, the flatter, sharper edge of the Manson/Rocna blade will penetrate where the Delta or Spade won't.

That's because the Delta/Spade have a triangular wedge 3-D cross-section (due to the weighted tips) that whereas the Manson/Rocna blades present a smaller flat cross-section. The Manson is the sharpest (by far) and is the best in penetrating hard-pack and grass, IMHO.

I've owned all of the above and used each for at least 3 years.