The folks at the violin shop I go to now recommended the Planet Waves egg-shaped one. I have the large one. Just got it a week or two ago. Seems okay so far. Come to think of it, I have to refill it. Thanks for the reminder.
I use two of the green snake-like things for my acoustic guitar. No problems. Just got to make sure there's no excess water in the snake or dripping off it. They're okay.
I also use a Radio Shack hygrometer that I got for like $20 for the guitar. I'm planning to get one for the violin too.
If this isn't the one, it's very similar to this one. Radio Shack Thermometer/Hygrometer
I might buy one of those Planet Waves ones for my acoustic guitar too. We'll see. Those green snake ones kind of come up short, I think. I'll have to keep a closer eye on the humidity in the case. This is the first winter for which I have them.