I have used them, they suck! hands down... They definitly look cool though, like glass bowls emerging from your soil, lol, i joked i was growing bowls as well.
But they hardly drip like it shows, after like a week their is barely any of their resivoir drained, the water just sits in it for the most part. I usually have to tap it or shake it. But it does give me a little reassurance when I am away, and one of my plants is a very thirsty girl so she gets that one.
I attached a pic with Andrea (thirsty girl) and her little watering bulb thing.
It was a gift, wouldnt buy one myself if I were any of you, unless you just think they look cool.
OB
You can see it in the corner to the left of the hygrometer
and notice how she still looks thirsty, shes never done drinking, and those clearly aren't working.