Hi,
Avoid having Material group is a release characteristics as in business may have minimum 200 Material groups to 1000 Material groups, if so how you design your release strategy?
Better keep release characteristics as minimum as possible for business, may be go for maximum 3 or 4 release characteristics such as Total value, Dcoument type & purchasing group etc... where later you can have considerable release strategies do design.If you and your business needs, then can have release characteristics CEBAN-MATKL and add this to release class and then design your release strategies by adding value of Material group
Regards,
Biju K