I don't remember what the R-4 looks like, but I have a much used and abused R-6 that I love. It's very much like a very beefy SARGE knife. I know a lot more about the history of the Sarge:
Basically, the Himalayan Imports SARGE is a small belt knife designed and crafted by our good friend Kismet. He made it out an old file, a spoon handle for the guard and some antler for the handle. It was dubbed the SARGE in honor of our forum friend and absolute good guy Silver Falcon (not spelled that way, but the exact name escapes me) who was a seasoned military man who went by Sarge to all of us lucky enough to call him our friend. Sarge is a Renaissance kind of guy when it comes to outdoors stuff. Kismet's SARGE seemed to not only be the kind of knife Sarge would use but would also be the type he would make for himself It's a handy enough design that even Andy Roy of Fiddleback Forge makes his own version of the KPH
Yangdu had the kamis crank out some of their versions of Kismet's knife (which is also known as the Kismet Practical Hunter because even though HE won't take credit for it, it really is a fantastic design). Several small runs of the HI SARGE popped up for a couple of years. Not too long after that, the R series started to show up. There were a wide variety of designs in that family of blades. You'd see some that looked almost Finnish in design, some that looked like a Schrade Sharp Finger, and even one that looked like a Klingon's skinning knife. One of the more popular ones was the r-6. The R-6 took the basic blade shape of the SARGE/KPH and married it to a full tang chiruwa handle. It resulted in a knife that probably wasn't as graceful or Elmer Keith-y as the KPH, but it IS a stout as hell pry bar.
Very neat knife indeed