I have a smallish mouth, and these didn't look as subtle as I wanted them to- if you want something subtle, try the Sweetheart fangs by Scarecrow.  However, they stayed in great, and I'm still using them years later.  They were fairly comfortable to wear and didn't come loose unless I wiggled them.  They are definitely very prominent- I wanted something that would show up when I smiled, but these were so big in my mouth that I had to bare my teeth for the whole "vampire fang" effect- otherwise the bottom part of the fang was below my lower lip.