They don't do @#$% for accuracy (unless your current pins or hammer/trigger are already out of spec and having a negative impact in that area already which isn't correlated to the KNS pins themselves, just the difference between garbage parts and spec parts).
As for whether or not they actually prevent or otherwise minimize wobble-out/ovaling of FCG pin holes in your lower...yes, at least in theory and at least to a certain degree. HOWEVER, even with many thousands of rounds downrange on a couple different large-frame AR lowers of my own over the years, and countless thousands more (much more than the large-frame guns) on many other AR-15 lowers I own or have otherwise worked on, I have yet to see ANY semi-auto oval out the FCG pin holes in a lower that weren't attributable to poor/ill-fitting parts or shear stupidity. Now...the same can't be said for FA lowers where, not only are you dramatically increasing the amount of wear/tear on your components, but you have many hundreds, if not thousands, of times more money invested in them so a ~$30 pin set is cheap insurance to help curb or eliminate the problem. However, there are more than a few issued service weapons in existence that have had the ever-loving @#$% shot out of them and continue to have FCG pin holes in their respective lowers that are free from damage.
It really comes down to whether the ~$30 is worthwhile to you and if you believe they'll help you sleep better at night knowing that your rifle has some sort of added (whether wholly unnecessary or not) protection against damage. The other thing to consider is what trigger will you be running? There are high quality triggers in existence that bear specific warnings AGAINST use of the KNS pins (Geissele for one). Keep that in mind as well as you weigh your decision.
