I use the thin stamped steel ones like the ones sold by MRC and PKT. They bolt to the floor pan and not the chassis tabs. That way you don’t bend chassis tabs, stiffen anything and they have more ground clearance and don’t bottom out as easily.
I got to say I love the KartLift Protectors. I did not think they were going to be durable, but I am already on my 3rd season with them. Just optionally replaced the one under my nose as it cracked. It was still functional and I will never run a kart without them. They definitely add longevity to a frame.