It has been used a lot recently, as a number of us want all our races maxed, and we hit Raps for one reason or another, at about the same time.
As for sound Vs. graphic, for me, I find the graphic to be more liable to get people killed. I know it's how I killed them most often. The graphic also prevents it from being able to get out of tight spots. The sound tells you they are in the area, but just look at how hard it is for MANY people to find a vaga when someone says "they are right next to my chat symbol, right off the ground". MANY people who play here can't fathom how to find something they can't actually see, no matter how explicit of directions they are given. The graphic, however, tells you exactly where to shoot.
For Pred Vs. Raps, that's say Rush Vs. Ambush. Sure you can use both races for the other, but they take different play styles. You don't rush with this race. You stay out of the way and wait until someone comes by and pop out for the kill. Or wait around a corner and stab people who turn it.
But, overall, my only complaint about the race is that it's slower than vaga. Granted I have that same complaint about all 3 knife races, but still. The graphic is only visible from so far, so as long as you have cleared the enemy out, you're safe. This race isn't made for taking on the horde.