They look to be similar to the one's Ruth Niles ells, but a little cheaper. However, you have international shipping.
If you are looking for a good deal on SS bottlestoppers, check out this current Group Buy - http://www.penturners.org/forum/showthread.php?t=65503
Ruth has a deal on her site for the mandrel, tap, drill bit and stoppers. Her stoppers are really nice to work with and it is her design, if I am not mistaken. It would be worth your while to check out her site.
I have used them for almost 3 years. The silicone rings are still in great shape with no cracks, etc. Ruth does sell a mandrel that has an MT#2 taper and it has the size needed as a part of the mandrel so no bushing is needed. The blank when drilled with a 5/16 will thread onto the mandrel and not slip when turning. No discoloration of the metal has occurred.