Better Beamer works exactly as described. It has really helped me improve the quality of my shots, especially on overcast days. On normal sunny days, I use the extender for "shadow: captures and it works far better than post processing. I received superb help from customer service in determining which version would fit my old but still useful Canon 420 ex flash. Really appreciated the assistance and the delightful attitude that accompanied it.
The Better Beamer is the best "High rate of return item" I have found in digital photography. Less than $40 buys anyone some really good shots and higher keeper rates.

Advantages: Focuses the light where you want it to go. Hard to describe how much better it is than simply using a normal flash.

Disadvantages: It is one more piece of equipment to manage.