I used the Fisheye Fix LED focus light, which appears to be a dead ringer for the Fantasea Nano, for a trip to Bali last month, and really enjoyed it. No problems whatsoever in 32 dives. First time using a focus light for me, so it was quite a treat. Smaller camera, though. My buddies with DSLRs all had the Fantasea LED 360
(or was it the LED44? I never found out for sure), which was MUCH larger and put out a MUCH larger circle of light, but I think that would have overwhelmed my poor little camera. I did prefer the AA's used by the 360, however, and wish my light used that instead of AAAs, so I didn't need to manage multiple battery types on the charger.
The Fisheye Fix Mini LED focus light
and the Fantasea Nano Focus light
both use AAA batteries, however, not AA. There are a number of websites out there that do not accurately quote this information in their specs, I've noticed, including the manufacturer's site (in the case of Fisheye). Whoops!
Interestingly, the guys at Reef Photo told me they didn't carry the Fantasea Nano because they had so many units that were bad and/or leaked immediately when they were testing them. They carried the Fisheye version instead, and said they have not had any reports of issues. Seems odd considering it seems likely they're both made by the same OEM, I'd assume, since they seem identical, but there you go. Reports in this thread do seem to back up their report.