I've used them. I like them. I have sets for wide-mouth and regular-mouth Mason jars. I think they work well. One word of caution: they do allow "burping" out the pipe top, and some liquid as well as gas may escape. To be safe, put your fermentation jars in some sort of containment. Here's what I did last February.
Edited to add: I too like the ability to ferment in small batches. Quart-sized jars work well for me. Note however that there are also half-gallon and gallon Mason jars with the same top size, and the Pickle Pipes will work on them as well.
