Ahhh yes the Muwwahids (just that). They were terribly fun to play with.
Not really any great stats, a little on the offensive side, a superb charge and stellar morale. You never knew what they might end up doing in a battle, much like a version of Ghazi with a bonus facing cavalry. Dead fun!

In RTW I found out along with many other (independantly) that cavalry charges had little to do with the bonus, and a lot more to do with the weight of the horse and apparently armour (as tests showed that Cataphracts had a quite stronger charge than Cappadocian Cavalry, where the difference was 4 point lower armour for the Cappas but having a shield of similar value instead).

Apparently the armour-part of the charge has been removed, but now all horses seem to have an equally strong charge (but difference in survivability in said charge).