My personal experience :
sound modules are great for home/studio use, but not for live playing.

The nice thing about arrangers is that you can select a style, a sound and then start playing. A sound module breaks the flow, as you have one more thing to take care of.

But if you are the kind of player that likes to program, setting up each song at home to send the proper patch changes, a sound module may work very well for playing live.