Not an issue at all on the trail, in fact vehicles with lots of squat tend to be really capable off-road. Rock crawlers and Desert racers have tons of squat.
Squat (or I have heard it called "dive" by racers) is more of a control issue on the street during hard breaking. Too much anti squat is worse than not enough, because it tends to cause wheel-hop. Squat in the rear of leaf-sprung rigs is bad because it can cause axle-wrap, but coil sprung Jeeps have no issues that I am aware of. Most of the beefy suspension components that come with modern lift kits are more than capable of handling the stress of Squat during hard breaking. RK claims to have really minimized squat with the plus kit, but to be honest, how many people running other kits ever complain about squat? I don't think I have heard anyone complaining about it.
If I paid for the "plus" kit, I would wait for the missing part and install what I paid for.