I use one religiously. Its a wonderful tool and has prevented me from making some stupid mistakes. (like leaving the salt out of the brine - yeah, I'm talented
)
When you get yours do a search for one of Chuckwagon's posts on their use. He included an information attachement to his post that is very helpful in really understanding how it can be used.
BTW - while you are waiting on yours to arrive it would be helpful in the long run to find a graduated cylander about 2 inches in diameter and a foot or so long. Many times I've run into instances where the brine isn't as deep as the salinometer is long. I'm sure you will run into the same problem and this is a wonderful solution.
Patience please, I'm just trying to get on the learning curve.