Many people we know have had good success with this unit and it highly recommended it.
It was more expensive buying it at Island Water World in St Maarten than purchasing the same unit online, but 1) they had it in stock; and 2) with the extra cost of shipping the unit to St Maarten, the savings wouldn't be worth it.
We were busy getting ready to go sailing for a couple of months so I put off testing out the unit. When I finally got around to it, I put the mini CD in my MacBook (which I had bad feelings about) and I had the problems of removing the small CD from my Mac which was described in an earlier post (see here).
Our external DVD drive didn't want to read the mini CD, so I put the box in a locker and forgot about it for awhile.
I came across the unit yesterday and decided to deal with it. It took a couple of hours of searching but I came up with the user manual (download it here) and also found the necessary driver which includes the utility software, plus an uninstall (download it here). We have OSXv10.5.3 on our MacBooks so we downloaded this one: Realtek rtl8187l Wireless Driver 1.309 Mac OS.
I read the manual, installed the driver and tried the Alfa wifi adapter and HURRAY it works GREAT.
Hope this helps those who are looking for a highpower USB wifi adaptor, and also those of you who can't load their little CD with the manuals, drivers, and utilities.