I feed the big round bales to the horses, but the goats have the hay off our fields. I have just about used the hay now, so the goats are having haylage and they love it. The only thing is, whereas a bale of hay you can open and it does not matter how soon you use it, haylage does go off once opened. The commercial bags (by that I mean the ones specially bagged for horses etc, with the manufacturers name) say use within 5 days. The ones made on farms, just wrapped in green or black wrap, I reckon 7 days use by. Our big bales, we try and use between 10 and 12 days.
If any of the bale looks a funny colour, or has a really bad smell then don't use it - it can be dangerous if it has fermented. I would introduce Molly and Milly gradually to haylage, by mixing it with their hay to begin with, like with any new food, so as not to cause any tummy upset. I am sure they will like it though.
I do find the small bales quite expensive, in comparison to hay, and its only because we have big bales in for the horses that I give it to the goats at all. Having said that, it does fill them up, so maybe you will find you do not use as much.
Oh, and it does have quite a strong smell, so be prepared for everthing to have that distinctive smell - but its much better than the smell of a billy goat of course!!!