I didn't consider this to be an essential upgrade until I had to buy one as my stock knuckles had too much play.
Of course it did tighten up the wheels a lot but I also realised that it didn't had 2 long "splines" that was on the stock design. These splines actually restrict the amount of steering angle that I can get even though I upgraded the whole steering kit on my E10. After putting the new knuckles, I was able to increase the amount of steering angle and this helped with my steering corrections when I on the verge of over/under steering.
Bottom line is that I'm adding this as one of the essential items to get as part of the steering upgrade for the E10!