I just looked at Sci-Fi lasers site, and it states that the SF502B can use 16340, or 18350 batteries.
Personally, I would go with the 18350's, but that is your choice.
The site you linked to (Lighthound) for the 16340's, shows that they have two different AW 18350 unprotected batteries; both cost $7.99 which is $1.00 more than the 16340's.
One listing says 800mAh, and the other says 700mAh, but both pictures show a 700mAh battery, not sure if it's a typo or what? You may want to check with them before ordering.
Edit: In the description of the 800mAh battery it says "new upgraded version" That's the one I'd go with.