we've used one from about 4 weeks or so ... DS just loves sucking, and would nom on my finger for litterally an hour of more, until my cuticle was half way to my elbow, and I decided that enough was enough, and if he needed to suck, he could have a dummy ...

now, he has it on and off during the day, and normally (but not always) when he goes to sleep.

but we watch him during the day, and if he's clearly happy we take it out, so that he's used to being without it IYKWIM

and we're trying to phase him out of it now ... would love to be dummy-free by 6 months, but aren't going to get our knickers in a twist about it, if he has it longer ... 12 months, 18 months, not sure what our "cut off" would be, it will depend on DS and what he wants it for and why, I guess.

But I see it as an appropriate tool at the moment, while he likes to suck but isn't hungry and is too little to understand that there are other options