BUT THERE IS ONE VERY SERIOUS PROBLEM!!!
If you create catalog system with lots of extra fields (40+) it will dramatically slow down your site in category view. Even if you create custom template to show only few extra fields in category view. The reason of this (I think) is the way extra fields are stored in the database. All of the extra fileds for an item is stored in one database field. If you display for example only 5 extrafields from 40 for each item in category view the system will looping through all extra fields because they are stored in one database field. I tried to get help from developers but there is no answer and no solution. The extra fields would give the real power of a CCK but this way it unusable for items with lots of properties. I hope this will be fixed if so this will be the number one extension.