The Historical discription for these units seems to be incorrect. Specifically this passage,

"Historically, the Goidilic tribes adopted ponies as mounts in favor of heavier horses and chariots, generally (some chariots and larger horses were used) because the ground of Ireland was too wet or rocky for a chariot or horse to move over swiftly."

This is untrue as the irish were famous for their chariots and charioteers. In fact many of the stories of ancient irish heroes such as Cuchulainn specifically speak of their awesome chariot skills. The Irish were still using some chariots when they were raiding roman britain(200-500AD), transporting them across the sea in small boats called curraghs. It's thought that the gaels didn't begin to phase out chariots till they realized from contact with the saxons that cavalry was cheaper and more manuverable to use. The Irish didn't full phase them out till around the 7th century.

Also the celts were famous for their chariot making skills and had possibly the most advanced and finely crafted chariots in the world. The Celtic chariot was drawn by a team of two horses, and measures approximately 2 m (6.56 ft) in width and 4 m (13 ft) in length. The one-piece iron rims for chariot wheels were probably a Celtic invention. Apart from the iron wheel rims and iron fittings of the hub, it was constructed from wood and wicker-work. In some instances, iron rings reinforced the joints. Another Celtic innovation was the free-hanging axle, suspended from the platform with rope. This resulted in a much more comfortable ride on bumpy terrain. There is evidence from French coins of a leather 'suspension' system for the central box, and a complex system of knotted cords for its attachment; this has informed recent working reconstructions by archaeologists.

According to Julius Caesar the Briton celts were the greatest charioteers in the world, capable of doing things in chariots other civilizations would not even try or think possible. So why the downplay?