I have an Arkel bag but have to agree that in dress clothes it would look completely out of place. It has been super durable but it's not exactly a good looking bag.
I'm not sure what options there are that will securely mount to the bike while being able to hide the mounting hardware. I have to agree with the poster above that the buckle mounting system on the leather bag would be frustrating and wobble around, but the bag itself looks beautiful.