The Dunedain Spearmen are cheaper and have a bigger battalion than the Rivendell Spearmen but have worse stats. They can be recruited from Imladris' Outpost expansion, the Dunedain Outpost once the troop tent has be purchased.
Flank Defence - Pikemen are used to defending from all sides when battling against monsters and cavalry. As a result, they cannot be flanked. They take no extra damage from being flanked and deal full revenge damage regardless of the direction they get trampled from.
'The Dunedain aren't upgraded like the elves are, and the upgrades researched at the Imladris Forge do not apply to them. To upgrade the Dunedain with Forged Blades, a level 7 Halbarad must be nearby to the battalion.
To upgrade the Dunedain with a Banner Carrier, a level 5 Halbarad must be nearby to the battalion.
The Dunedain Spearmen come in a battalion of 10 soldiers. Their recruitment cost can be lowered by building Hobbit Farms on settlements. They are not as powerful as Imladris' elven units, so by themselves, they won't last very long in a fight. However, because the are half the cost of Rivendell Spearmen, it is worth it to invest in a Dunedain Outpost. To increase their durability, it is essential to recruit Halbarad as well and level him up quickly; once he is level 7, the Dunedain Spearmen and the other Dunedain units will be able to purchase all of their upgrades. He also offers them a leadership bonus, so it could be a good idea to keep them close to him. With the Master Ambushers ability at their disposal, you'll be left practically begging enemy cavalry to trample your Dunedain Spearmen.