The reason it gets 4 and not 5 stars from me is that it is a way-too overpriced for what it is and the value it provides. I take it as a charge for an innovative idea!!

Advantages: 1. When used properly, it definitely accomplishes the purpose it claims to serve.
2. Ease of fixing on and removing from flash; but this also leads to a disadvantage of sorts as described below.

Disadvantages: 1. I have to always hold it pushed upwards to keep its position parallel to the lens. Otherwise, the line-of-sight of the lens and beamer cross at a much shorter distance than where the subject usually is, leading to sub-optimal results.
2. It is pretty common for a lot of us to use two bodies out in the field. As the fixing mechanism on the flash is flimsy (while easy), there is always a chance of it falling off, if it is on the camera+flash not in use (usually hanging on my body).