The Firebrand Buggy is an upgraded version of the Twisted Dawn-era Recon Buggy. It boasts a closed cockpit for better driver protection, and a rotating weapon system, most likely remote controlled. It is possible that it was designed and built in the inter war times, and was a replacement for the Recon Buggy. However, it was phased out by the more advanced Viper Drone.
The Attack Buggy is a crate unit that can be found in any standard game mode.
Before version 0.9, this unit was called the Attack Buggy, and in terms of gameplay was identical in every way to the Recon Buggy, apart from the updated Voxel and aforementioned rotating turret. It was unbuildable but it had the same price as a Recon Buggy in the Rules.ini.