This specific option will actually come with the buffer tube necessary for installation, so you do not need to worry about buffer tube compatibility. The gas system will not have any affect on the actual buffer tube and instead it will affect the buffer weight and spring which is not included with this pistol brace.
The gas system is on the barrel. This is a carbine length buffer tube, which is fine for what you want. I'm running a 300BLK with pistol length gas system and this brace/buffer tube combination.