So I bought a brush guard.....

[1engineer]

I left ARB in 2005 so I'm going off 10 year old memory here and I can't give you any detailed data. Like I said earlier, structural strength improvements to the front of the vehicle can, but not always, cause higher deceleration forces during an impact. Steel replacement bumpers effectively remove crumple zones and other deformable materials that absorb energy and reduce deceleration. The differences can range from none to significant, but cause the airbag to deploy when they would normally not be needed for an occupant wearing a seatbelt. The SRS system cannot compensate for a bullbar because it doesn't know it's there. As far as it knows, there is still 10 inches thick of deformable stuff to slow the vehicle down first before it has to spring into action.
Every model of vehicle was different, and factors included the vehicle mass, chassis geometry, sensor style and location etc. I think the Suzuki Jimny bullbar had no 'ripples' in the mounting brackets and bigger vehicles needed three.
ARB bullbars are very well engineered and suit most offroading needs very well, but I dont think they are the best choice for serious rock crawling and majorly technical type stuff. They're primarily designed to protect the vital parts of a vehicle in an animal strike, provide protection to body parts from low speed offroad hits on trees and the like, and to provide platforms for fitting other accessories like winches and lights.

He's right.

Let's use our imaginations for a minute: Let's say I have a bumper that extends out 10 feet in front of the vehicle and that space is filled with foam. I hit a wall at 15 mph. Chances are my airbag will not deploy. In your stock vehicle your airbags only have a few inches of foam and chances are they will deploy. If you have a modded steel bumper (non ARB) I guarantee your airbags will deploy. Why? Deceleration and energy absorption. In any higher speed accident it really does not matter because the deceleration rate of the vehicle will be high enough to set off the airbags and the low speed or lower impact (hitting a deer) protection you have with an aftermarket bumper is non existent. You hit a pole at 50 mph I don't care what bumper you have, your airbag is going off. At higher speeds the vehicle is designed to crumple much further back than just your bumper and dissipate as much energy as possible to protect the occupants.

Bottom line: Your bumper choice will affect the ultimate operation of the airbag at lower speeds. At higher speeds? Not so much. Brush guards? The airbag sensors won't even know you have a brush guard.