I have plenty of experience with Acesonic. As a standalone, physical media-only player (like the one you linked), they fit the bill fine and perform admirably.

If you are looking for hard disk storage, I would strongly recommend going with a real computer solution, or possibly even an iDevice. I guarantee you that a client will find it easier to use than the Acesonic -- somewhat counter-intuitively, as you might think a standalone device would be simpler. But adding new media, setting the queue, searching for songs -- you end up wishing you had an internet connection, a search box, a mouse, and a keyboard. Trust me.