Here are my complaints:
Liquids: The central pillar is so short, it can take only very limited loads that have a lot of liquid. It is quite unsuitable for puréeing soups and similar tasks, because it leaks all over the place. This is no longer a problem for me, as my new Mixie is very good at that sort of work, and much easier to deploy, store and clean.
Size: For so many jobs, it's just too large. The Mini-Prep gets used more than 20 times for every time this machine gets used.
Vegetables, etc: When chopping vegetables, salads, or meats, by time it has them even, they are chopped too finely. I prefer to cut by hand so I have control over exact textures and sizes, and that's a lot easier to clean up after too.
Bulk / Weight: I don't have infinite counter space, so this machine must be kept in an under counter cupboard. It is very heavy and very bulky, so difficult to store and difficult to deploy.
Cleaning It is much more difficult to clean than other tools I have. The plastics are quite complex with a lot of places that are hard to clean out properly.
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