I owned dual Nano's and had a fairly positive experience. They're a dramatic improvement over a camera's internal flash, but there are some major drawbacks:
- Syncing with Camera is unreliable - Fantasea has not done a good job of perfectly matching the fiber optic cable attachment point on the flash housing with the flash's little sensor... it is about 1cm away. This can lead to pretty touchy reliability and the strobe may not always fire when you want it to.
- Strobes are not compatible with all cameras - Despite having 3 different sync settings, the strobe is not necessarily compatible with your camera, and the only way to tell is to actually get a unit and play with it. It was compatible with my Canon Sd1000, but when I upgrade to a Canon G9 I was disappointed that the camera could not trigger the strobe and was now forced to buy new strobes (S&S YS27-DX, which are great).
- Battery life is okay - I used high capacity rechargeable batteries and could only get 1 dive per set of batteries. With regular non-rechargeable batteries you may be able to get 2 - 3 dives out of it. (With my new YS27-DX's I can get 4 dives out of it, though it does use 4 AA's instead of 2 AAA's)
- Too Few Flashoutput settings forces you to use different diffusers - The strobe has only 3 output settings to determine the brightness. If you need even less light or you need it to reach farther with less intensity then you have to use the supplied diffusers, which come in 3 levels of opacity - it's just one more thing to consider and can be a pain to change underwater in a stiff current.
All those things said... the nano is a good starter strobe, especially for the reasonable price. However, if you see yourself getting remotely serious about it, do yourself a favor and invest in a little more expensive strobe.
BTW, I've dealt with Fantasea's customer service several times and they have been FANTASTIC. Good solutions and good response times.
Good luck