The lack of a rubber seal that will age and eventually fail, or provide any unwanted taste to the heated coffee. Large open tops on the decanters making clean up easy.
Negative Product Points
While the Rubberless models will have a water seal on the ground glass areas where the decanters mate, the lack of a rubber seal provides the least desirable vacuum pulldown of the different glass brewers. The thin necked Silex models with the smaller rubber seal have superior sealing and pulldown. The large necked varities of Silex with rubber seals have a lesser sealing ability than the thin necked Silex but better vaccum ability than the Cory Rubberless models.
Handling of the two decanters when mated requiers greater care, as the rubber seal on other varieties provides a cushion against banging the glass together.
The Cory Rubberless models came in three sizes, 4-6 cup, 7-8 cup, and the family size of 10-12 cups. The manufacturers cup ratings are for about a 5.5 oz cup size versus the normal 8 oz size that is typical. So the realistic number of regular cups of coffee will be about one half of what the manufacturer specifies. The price for the Rubberless models is based on the coffee tasting better due to the lack of a rubber seal. The hype is unrealised as the coffee will taste the same on any of the glass brewers. Due to the hype the prices will run in the $40-$60 and up range for an 8 cup model. The smaller and larger models will be priced higher by collectors due to the scarcity of these size models.
For the average user, the water seal is the least desirerable for final pulldown. The Silex large necked models are half the price and with a good seal will achieve a faster pulldown. Look for these models before spending the bigger $$$ on a Rubberless Cory. These are for collectors or snobbish users :-)