I have the KartLift Brand and I have the long ones on my Son’s Tony Kart and I promise you they are by far the best plates to put on your kart.
I also heard that skid plates change how the chassis handles but I was told by many that the KartLift brand doesn’t change how the chassis handles because they Free Float. I’m not sure how they free float but they did not change how his kart handled at all.
In fact my son won his class Championship this last year and the best part is there is not a scratch on the bottom of his kart.
So I would say go ahead and get the skid plates but make sure you get the KartLift Brand as I know for sure they don’t change the handling at all in the kart because of the Free Floating design.