I think you need to be guided by your baby tbh as to when you take it off them (assuming they will take it in the first place). Your baby may also decide for themselves that at X months/years they no longer want or need it.

We use one with DS but he came out and put his fingers in his mouth straight away. He is also a bit chucky and seems to need to suck for a few mins after most feeds (but without feeding iykwim?). He also uses it to go to sleep and I have used it to calm him down when he is distressed.

We have been advised that the cheaper dummy styles are the 'best' in terms of shape. Apparently the orthodontic ones aren't great and can cause more problems with bfing etc. Not sure how true that is, just what we have been told by midwives and also a dental technician at mothers group said the same thing.

Good luck with the whole dummy thing. It is a good idea to have a couple on hand but I think it's like the rest of having a baby and entering parenthood - it's one big rollercoaster ride and you can't predict now what will or won't work for your bub.