They're a work in progress and are currently under powered and hard to use effectively. I put them on fallow me and drag them behind the archers and charge them, then put them back on fallow me and so on. Think of them like a big clumsy boomerang. Also if I'm dehorsed they can come guard me or be told to dismount so I can take their horse. I never elect to make Cav and only take them from prisoners or rescues. I feel only horse archers and ranged foot units are functional enough to raise from scratch ATM, but I'll use anything I get for free.
Btw this thread would do better in the Citadel forum or it's single player sub.
This is tech support forum actually for "game doesn't run" "game froze" "thing doesn't work"type stuff.
Underpowered? They slide through formations holding spears without any form of collision. Against infantry they are definitely not underpowered. They might be against archers though, even full mail barding can't seem to stop an arrow.