I'm not saying you can't or shouldn't race with a Slash but it's sort of like trying to do rock climbing with a Geo Tracker, sure it probably can do okay but there are vehicles that are better suited for doing it.
You realize he is putting this in a Slash 2wd and not an E-Revo or Arrma Kraton 6s right? 500oz/in of torque is way way overkill for the Slash it would probably break the bell crank. For the Traxxas 2wd vehicles unless he is racing, which idk why he would be using a Slash for racing, the Amazon...
Best bang for your buck servo in my opinion. I run these in most of my 1/10th scale vehicles. I have some that are 3+ years old and still going strong...