They all work and they all sometimes don't give the blood trail that you want. I base my opinions on past experience and have taken a ton of game with all types of heads over the years and all of them if well made and sharp as well as put in the right place kill and sometimes they just don't always bleed. I took a whitetail once from a stand, at the shot the three blade Woodsman thumped through the deer like a watermelon. Hitting mid lung on one side exiting out the bottom right at the elbow of the shoulder. With this shot and exit hole location the razor sharp three blade head sticking three inches into the ground, there wasn't a drop of blood at the shot other than on the arrow.
I called my wife on the phone to come with help and a camera because we were in for a short blood trail. I watched the deer run about twenty yards and jump a fence into a bedding area. I thought I would follow the blood trail to the fence where it crossed and wait on Lisa to get there. Well there wasn't a blood trail either, not a drop. I couldn't believe it.
We began searching in the direction it ran and soon found it about another thirty yards away. When we found it I told Lisa to wait for me at the deer while I went back and follow the blood trail from the body that I had obviously missed. I looked and looked but there wasn't a blood trail, not a drop.
Once field dressing the deer the autopsy revealed that the shot was exactly like I had thought and all the blood was in the body cavity, all of it. I would have bet that you would have been able to follow that blood trail from fifty yards away, but not the case.
On defense of single bevel two blade heads, I have been using them for the last three years. Taking elk, several wild hogs and a hand full of big game animals in Africa with them. Almost all animals were taken with sinew backed osage bows and a few were with glass backed longbows all 60 lb bows. Almost all including the elk and African animals were complete pass trough's. All also resulted in either a very short descent blood trail or falling dead in sight. In every case except one, the Gemsbok in Africa the animals were hit with perfect shot placement. So the head really didn't come into play in my thoughts. The Gemsbok however, the shot placement was perfect. Tight behind the shoulder, mid lung. BUT it centered a rib. At the shot I saw that I only got about half an arrow penetration and it was getting dark. We went back the next morning finding the animal less than eighty yards from the hit. Once skinning began we found that the arrow exactly centered one of the heavy rib bones. The heavy 850 grain arrow still had enough energy to punch through the other side, just cutting the hide on the off side and leaving a bloodshot bruise the size of a base ball on the hide. This arrow tipped with a 185 grizzly and a 200 grain woodyweight shot from a 60 lb bow was the only reason that I had enough energy to recover this animal.
I think the main thing is to match the head to the animal you are hunting and hope for the best but prepare for the worst. SHARP and as heavy as you can shoot, both bow as well as arrow wise is the key.
The rest is just all advertising and there is no magical broadhead that will make you kill everything that you shoot!
But also in defense of single bevel heads I have been bumping up all my arrows weight forward with the Woodyweights and will tell you that they do perform better. I even shoot my arrows with field points with them and you will notice better arrow penetration on targets, quitter bows and arrows flying like darts to the target. In Africa I went extremely heavy on arrow weight. In testing out of my 60 lb longbows, I find that there seems to be a sweet spot at around 700 to750 out to 830 grains without sacrificing speed and trajectory. For me the best mix of weight and speed with performance seemed to be 750. I only went with the extremely heavy in Africa because I knew the shots would be limited to close range and I expected big heavy boned animals.