They look very different from one another.

'Hameln' is a smaller plant, generally 2' x 2' in size, with ~1/4" wide leaves. It tends to hold it's flowers higher off the plant, and blooms earlier than 'Moudry.' It is a lighter green color, and looks more like a traditional Fountain Grass in habit.

'Moudry' is larger (3' x 3') and has ~1/2" wide dark green leaves. It's habit is more like a mound or tussock than a fountain, and it's flowers are larger and darker in color, and held more closely into the foliage.

They are both great grasses, but if you grew them side-by-side, you wouldn't think they were in the same species.

Moudry also has a bad reputation for self-sowing vigorously in warmer zones (yours) and Moudry is not nearly as hardy in the colder zones (zone 5 & down). That said, I love the leaves on Moudry, very swishy :o)
A.