I bought some when DS was a couple of months old and have tried them a couple of times with no success.
For a start the non feeding side fills with milk each time, and if you're lucky this is only a problem when you need to take the lilypadz off to feed on that side and have to catch the milk in something. If unlucky it explodes out itself, soaking you...
If they do control the letdown for you how do you manage feeding in public? Where do you put it while feeding and how do you get it back on again afterwards?