Not sure where you are located and the types of matches held in your area, but my take on this shotgun:
In general you will be asked to load your shotgun to division capacity.
In standard manual (pump shotguns) it is typically 9 total in your shotgun.
This takes away your capacity advantage as we will all start with the same number of shells in the gun.
I haven't played with the KSG, but looking at vids on how it works, I know I would be faster reloading a conventional style shotgun vs. the KSG.
Therefore overall I would be faster through a course of fire with another gun.
Reloading the KSG while on the clock would be interesting to say the least.
The only place the KSG may have a chance of being competitive would be in Open division where you can load up the full 7+7+1 in most scenarios.
But again, I have a pump that holds 11+1, and I know that I can reload it faster than I ever would the KSG, so while you may start with a 3 shell advantage, I would overtake you during the reloads.
I can put 8 shells into my shotgun in about 4.5 seconds, if not less.
There is no way I can think of to do that with the KSG
Would it be fun with the KSG, sure it would.
If you intend to be as competitive as possible, there are better choices.