With IDM is it recommended to use auxiliary attributes ?

In production we have extended some attributes of the user class nd
works very well, but I am told it's not a good idea to extend base
schema class. We are currently evaluating more attribute extensions and
have been testing aux classes with mixed results.

Mapping eDir aux and JDBC attributes is confusing for starters. The
database has 2 tables which idm references, one for users and other for
groups, and these link up to the user and group class in eDir.

How does the aux class fit into this model ?

I've added it as an additional class, and added the attributes in the
filter. I have two aux attributes, one works and the other doesn't.
Both attributes also appear in the user class filter.

In the matching rule, I don't understand the whole class attributes and
Non Class Specific attributes. The attributes appear in the User class
(in production), and now they only appear in the Non class specific (in
testing). I don't know why this is the situation, or how to make them
in the user class if this means anything.

Gone back to the start via VM and snappshot and recreated everything
using base class extensions and no problems what so ever.

Any tips ?