Any of the systems that depend on the coach air brakes will not work on a gas chassis without the addition of an auxiliary air compressor on the coach. There is one system that does have that option, but it was far more expensive than the US Gear system when I was shopping. I have four cross country trips, over 30,000 (we take the long way) with the US Gear system and would not want to be without it.
Brake in box systems are fine for people with multiple cars to set up to tow, but they are a bit more of a hassle to setup and take down. Especially if you need to break down the tow in traffic it could be a real pain. Don't ask how I know about breaking down the tow in traffic
Paul