I purchased these for use with my Avent Natural bottles, since the original discs are incredibly hard to find. These do do the job, and the slight discoloration over time does not hinder function. They do allow a few drops past between the ring, lid, and bottle, but not enough that I've had an issue- just a bit sloppy when opening to put a nipple into use.-I primarily use these after I pump, but do use these once a day to prepare preemie formula.-Picture shows comparison of Avent disc and May…