I have been sounding for many years and have found that these are the best thing I have found.
They are flexible, can be left in for easy stretching, are 16 inches long so they reach all those GOOD places, and are easy to sterilize. You will want something longer than 7" once you get used to the intense pleasure of going deeper and these conform to your internal plumbing so there is very little chance of injury, they also increase one size in the middle for a better feel.
I have several sets of of metal sounds and have used the silicone ones much more since I got the first ones.
I love them.
Doc