i third the convienece of a thumb!!! DD1 was the best self settler with the thumb, but as a dental nurse i hated it!! i can see the damage that was done from the thumb, yes some people suck thumbs with not dental damage, but not all!!
we stopped DD sucking it at the start of the year, we used sports tape around her thumb so she couldnt remove it and it was uncomfortable to suck, it took a few weeks, the first few days were hard but she stopped, in reality it was pretty easy to stop her!