Review (4/5): I haven't had any problems with water getting inside..
After reading the reviews, I bought it and then bought the improved O-ring. But, I ended up with one that wasn't a good fit so, I went back to the original. Even with the original, I'm not getting any water inside of the battery compartment.
I've now had this for several years and it's working just fine. It does go thru batteries but I've been using rechargeable batteries. I like this system rather than one that's plugged in all the time because I don't have to be concerned with vampire power loss and I can bring it with me when traveling.