The US cartool ones use the floor as a structural plane, they are very strong when installed properly. There are a couple of 9 second rides running them, no issues.
I have a few sets I made from 2x3 and a set of US cartools. I'd use either without hesitation.
I like using the 2x3 if I'm putting a rollbar/cage in a car. Give you a place to land diagonal bars behind the drivers seat. No landing plate required.