Like its brother, the Sydonian Dragoon, the Ironstrider Ballistarius shares the same chicken leg design; however, unlike the Dragoon, the Ironstrider carries twin Autocannons or Lascannons, as well as downlinks providing the crew with the sum knowledge of their enemies, making it highly dangerous and efficient in eliminating important targets. These walkers travel along with their Skitarii Ranger brethren in search for high value targets. The Ironstrider's mechanized mounts are able to walk on the most hostile terrain, making it quick on uneven terrain even among other walkers. However, this makes the servitor driving the thing to be the first component to fail, if any other part of the fragile walker hasn't already been shot (or stabbed, or both). You would think the Mechanicus would spend some more time in making their slavebots more resistant to things such as corrosive gasses and water.
When in battle, the role of the Ironstriders is to act as a mobile artillery platform, basically making it a Dragoon with more Dakka. Due to the Ranger gunner´s enhanced eye sight, it is the role of an Ironstrider Ballistarii to hunt down enemy commanders and spiritual leaders in order to sow chaos and confusion within enemy ranks. When not hunting for a particular space pope, an overgrown fungus or psychic Harry Potters, the Ironstriders form into groups called a Ironstrider Cavalier whose sole purpose is to shatter enemy formations. The quick speed, agility and firepower of the formation ensues that no enemy, even ones clad in Terminator armor, or a Super-heavy tank can emerge unscathed.
Additionally, Ironstriders are able to see things in slow motion due to the combination of the downlinks mixed in with an intravenous dump of hyperfocus stimulants which hype up the already augmented senses of the rider. This ability is what allows Ironstriders to hit with such accuracy and grace that could rival even the smug knife-ears and their own chicken walkers. Thus it is of no surprise that Ironstriders are favored among the Mechanicus forces when out hunting for potential acheo-tech or a new STC.
Just to add a bit more of a grimdark flavor to this radiation-baked chicken (like we don´t have enough Grimdarkness in this crapsack galaxy anyway), canon states that when the servitor steersman of the Ironstrider eventually bites it due to how much physical stress is forced upon it (not counting the multitudes of things that can and probably will kill it much earlier on the battlefield), the perpetual motion engine of the machine keeps the walker moving along on a perfectly straight line, heading to God-knows-where. Once a lackey of the Mechanicus manages to catch up with the thing, they toss out the (at this point) emaciated and decomposing corpse of the late servitor and install a new one like a fresh battery.
It is worth noting that the lore actually addresses how someone manages to perform such a challenging operation on a constantly-moving contraption; the Tech-Priest stands on a floating platform called a grav-bier which keeps them steady as the machine walks along.