The material I made mine from was clearly different than George's based on the weight, but mine are close to 1/16" and 8" long from some unknown wire that came with our house. IMHO, they are OK for secondary guyouts. I would not use them for primary ones unless conditions were calm. For an A frame that would be just the 2 ridgeline stakes and maybe the corners unless you put these every foot along the edge like George did. I went with a half-pyramid pitch.
Even pushed in to the max, the hook can still deform with strong gusts. I've not had issues with hard ground (I assume you ground or filed a blunt point of some sort). Rocks and roots will obviously stop it. I usually try a slightly different angle then. I've always been able to get past whatever was there. Sometimes that requires grabbing it near the ground also to help keep from bending and jabbing it in and out a few times to break around the object. I've not tried frozen ground.
FWIW, I prefer a decent aluminum Y stake. I only use these homemade wire stakes for the 4 secondary tieouts but I've rarely used them. You can make several of these for the cost of a Y, but if you're often going to be going into really hard (or really soft) ground, I'd go a different route.
As an aside for those now finding this thread, you can see what I've done with Prototype 2.