if you do not want to maximize your threat put your hotkeys close together on your keyboard and just smash it with your fist / a hammer, but dont laugh at people who know the value of >100 extra tps (with just putting another ability in their rotation...)
I've just given up on it all honestly cause the risk vs reward of using rend just isn't worth it. If you can pull it off perfectly in the rotation when conc blow is down and shockwave is down and you have a single gcd before shield slam is up it comes out to a threat increase but any other time or a mistimed hit and it will be a threat decrease.
The initial math was strongly in favor of it but the actual execution is too difficult to pull it off. Its definitely something I will be keeping an eye on though with the better scaling and the potential nerf to deep wounds. For now it is just too much hassle for too little gain, we already have enough garbage to micromanage as it is.
Down the line when we start looking at future raid zones, higher dps weapons, and AP values I'll take another look at it. Based on the numbers it should scale up much faster so hopefully one day it reaches the point where it is worth using or is less picky about when you put it into the rotation.