I have both Devoto and Omer shafts. If you haven't notice the floppers on the Devoto slip tip and the 6,5mm shaft and omer shafts are the same. I really like these floppers, and like Baur said they are great for fish with soft flesh.
The low profile of the flopper will reduce the wound size when it goes trough the fish. A bad placed barb with a big profile will make a big wound on the fish and increase the chances of loosing it.
Other things that help is to file down the edges of the flopper, like Baur said, also of the flopper pin, and keep the shaft tip in good condition. Sometime a hit on a rock deforms the shaft tip slightly and that will so cause a bigger wound.
I've never caught a Dentex...I wish!
I've seen some of the Dapiran movies (5 starts) and was really impressed how Dentex trash around when they are speared.
One of my favorite fish to hunt are bluefish, and they also trash around a lot (the fish just go completely insane when speared) and have very soft flesh. The devoto shafts with “Low profile" really helped a lot in bagging some.
How you play with the fish and reel line is also very important.
First thing I try to do is keep the fish from bolting away and taking to much line with it. Second keep it of the bottom and from tangling the line all around the rocks, and try to keep the reel line as vertical as possible.
Sometimes this is just impossible and the fish will give no chance and immediately go beserk and try to get free from shaft rubbing himself on the bottom.
I usually don't try to grab big bluefish until they have run out of gas, that’s just too risky (they will bite) and if you didn't get any bone (a shot to the head or hard place) it will tear for sure.
the best luck for you guys with Dentex.