I have a Watson battery that came as a freebie from B&H when I bought my camera. It has worked fine. My impression is that it doesn't last quite as long as my Fuji batteries, but the difference isn't a problem.
I only have it because it was free and because it came from B&H which is a reliable business. Generally I avoid third party batteries. Having spent $700-800 on a camera I'm not inclined to try to save $30-40 by buying off brand batteries.
