The odd cheerleaders are nice for chasing routers and have somewhat of an impact on enemy morale if placed behind your spears. Apart from that they might be able to flank, but I'd use cavalry everytime - hands down. It's personal preference, I like screaming banshees on the battlefield just for the heck of it. But they are no game winners, far from that.
The Screeching Woman are prepared to reduce the enemy morale, no matter what.

Germania, for the win, needs to blitz against Brittania. If didn't, Brittania will be a pain granted for sure, plus the Gauls and the Julii which will be as powerful as a supernation.