I can't comment on the RD9, but I have put my BK9 through the paces, and it has come through with flying colours.
It has been batonned through dozens of logs, cut fuzz sticks, hacked through undergrowth, and always come back for more. No edge damage, and even after the hardest use, it returns to an impressively sharp edge after a few minutes with a pocket stone.
Once, I was on a fishing trip with some friends, on one of those nameless lakes that dot northern Ontario. We stopped for a shore lunch on a rocky outcropping, near a pine forest. We did up some excellent bass with beer batter. When we were finished our fishy feast, one of my buds had a momentary lapse in judgement, and tossed the contents of the frying pan across the rocks. Long story short, the cooking oil made a path between the fire pit and the dry pine needles covering the rocks. It took only a few seconds for the fire to spread to the point where it was almost beyond our ability to stop. A few of the guys attempted a bucket brigade, but the fire pit was so far from the water that this wasn't solving the problem fast enough. I had my BK-9 with me, and I used it (nay, abused it!) as a shovel to cut / dig / gouge a fire break between the burning ground and the forest. The area is mostly glacial lakes and pine trees, so the soil is only a few inches deep. I was scraping like mad, grimacing as the edge of my knife kept hitting bare rock. Anyway, the trench worked, and we were able to concentrate on putting out the smouldering dirt without having to worry about the fire spreading. It was a harrowing experience. When our work was done, we sat around, covered in soot, and had a round of victory beers. I took the time to inspect my BK-9, fearing the worst. As it turned out, I had chipped away a bit of the finish, and slightly dulled the edge. That was it. Five minutes with a water stone, and it was good as new, albeit a bit scuffed. And that was after scraping rock.
This is just one guy's testimonial, of course, so take it as you will - but if ever there was a knife I could say I would trust with my life, it's my BK-9.
Just my $0.02 CDN!
All the best,
- Mike