ICE-21 vs ICE-20
The Cuisinart ICE-21 is a newer version, it has the similar features as the ICE-20.
However, there are some design changes to the appearance and the mixing paddle.
According to users (people who own ICE-20 and ICE-21) reviews, the key difference between Cuisinart ICE-20 and ICE-21 is the paddle design. The manufacturer claim that the new mixing paddle design on ICE-21 makes processing time 25% faster.
An user also points out that only the freezer bowl are interchangeable, other parts are not interchangeable.
For the design difference and recipes, you can download the manual to get details:
Official Cuisinart ICE-21 manual download link: http://www.cuisinart.com/share/pdf/manuals/ice-21.pdf
Cuisinart ICE-20 manual: https://www.cuisinart.com/share/pdf/manuals/ice-20.pdf